Iridium-catalyzed Asymmetric Hydrogenation of Polycyclic Heteroaromatics, Pyrrolo/Indolo[1,2-a]quinoxalines and Phenanthridines Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-16 Shu-Bo Hu, Xiao-Yong Zhai, Hong-Qiang Shen, Yong-Gui Zhou
Owing to the reversible dehydrogenative rearomatization of hydrogenation product and poisoning effect of nitrogen atom, asymmetric hydrogenation of polycyclic nitrogen-containing heteroaromatics is still a great challenge. Herein, through in situ protection of hydrogenation products with acetic anhydride to inhibit rearomatization and poisoning effect, a novel iridium-catalyzed enantioselective hydrogenation of polycyclic nitrogen-containing heteroaromatics, pyrrolo/indolo[1,2-a]- quinoxalines and phenanthridines, has been successfully developed, providing a facile access to chiral dihydro- pyrrolo/indolo[1,2-a]quinoxalines and dihydrophenanthri- dines with up to 98% ee.
One-pot Synthesis of Alkynylated Coumarins via Rhodium-Catalyzed Annulation of Aryl Thiocarbamates with 1,3-Diynes or Terminal Alkynes Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-16 Yuan Gao, Fenfen Zeng, Xudong Sun, Minfeng Zeng, Zhen Yang, Xianqiang Huang, Guodong Shen, Yongsheng Tan, Ruokun Feng, Chenze Qi
A convenient and selective synthesis of alkynylated coumarins from various aryl thiocarbamates and 1,3-diynes or terminal alkynes via rhodium-catalyzed C-H bond activation has been developed. In this transformation, both symmetrical and asymmetrical 1,3-diynes could be applicable, obtaining various 3-alkynylated coumarins in moderate to excellent yields. When R1 is aryl group, the resulting compounds were found to exhibit intense fluorescence in the range of 412-443 nm with quantum yield of up to 0.57 in CH2Cl2. Moreover, the internal alkynes were readily converted to 1,2-dione, olefins, alkanes, and bisheterocycles under certain conditions.
Palladium-Catalyzed Regioselective Three-Component Cascade Bisthiolation of Terminal Alkynes Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-16 Huanfeng Jiang, Jianxiao Li, Can Li, Lu Ouyang, Chunsheng Li, Shaorong Yang, Wanqing Wu
An efficient and novel NHC(N-heterocyclic carbene)-palladium-catalyzed three-component cascade bisthiolation of terminal alkynes, K2S (potassium sulfide) and diaryliodonium salts for the assembly of functionalized (Z)-1,2-bis(arylthio)alkene derivatives has been accomplished for the first time. This unique observation features a broad substrate scope, excellent functional-group tolerance, and high regioselectivity. Especially, an arylthiolate anion from diaryliodonium salts and potassium sulfide was proposed as the key intermediate in the catalytic cycle.
Direct Synthesis of Sulfinamides by the Copper-Catalyzed Electrophilic Amidation of Sulfenate Anions Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-14 Junliang Zhang, Qiang Dai
A method for the construction of sulfinamides via the copper-catalyzed electrophilic amination of sulfenate anions using N-benzoyloxyamines as the amination reagents. This procedure featured with the capture of in-situ generated sulfenate anions from β-sulfinyl esters under mild conditions, which provides an efficient strategy for the synthesis of diverse sulfinamides in moderate to good yields.
Inexpensive Ruthenium NNS-Complexes as efficient ester hydrogenation catalyst with high C=O vs. C=C selectivities Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-13 Bernhard Stadler, Pim Puylaert, Justus Diekamp, Richard van Heck, Yuting Fan, Anke Spannenberg, Sandra Hinze, Johannes de Vries
Ru(NNS)(PPh3)Cl2 (NNS = 2-(methylthio)-N-(pyridin-2-yl-methyl)ethan-1-amine) was employed in the hydrogenation of α,β-unsaturated esters, reaching selectivities for the allylic alcohol up to 95% in the hydrogenation of iso-butyl¬cinnamate. In addition, several ester substrates were hydrogenated with catalyst loadings as low as 0.05 mol%. Surprisingly, selectivity of the hydrogenation of the C=O vs the C=C bonds strongly depends on the solvent.
Photoinduced N-methylation and N-sulfonylation of azobenzenes with DMSO under mild reaction conditions Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-13 Ning Xu, Yan Zhang, Wei Chen, Pinhua Li, Lei Wang
A photoinduced N-methylation and N-sulfonylation of azobenzenes with dimethyl sulfoxide (DMSO) was developed in the absence of an external photosensitizer under mild conditions. The reactions underwent smoothly to generate the corresponding products in high yields through a radical addition using the starting material azobenzene as a photosensitizer. This strategy features simple operation, easily available starting materials and DMSO acting as both methylating and sulfonylating agent.
An efficient and practical method for the enantioselective synthesis of tertiary trifluoromethyl carbinols. Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-12 Lorenzo G. Borrego, Rocío Recio, Manuel Alcarranza, Inmaculada Fernández, Noureddine Khiar
An efficient sulfinamide/olefin based chiral ligand, MetSulfolefin, has been developed for the enantioselective rhodium-catalysed addition of aryl-boronic acids to trifluoromethyl ketones. This shelf stable ligand is insensitive to air, oxygen and moisture, and it is obtained in only two high yielding steps from cheap commercially available (R)-tert-butanesulfinamide. The new ligand tolerates the use of hindered boronic acids and leads to the formation of a series of chiral trifluoromethyl-substituted tertiary carbinols in high yields and excellent enantioselectivities (up to >99% ee).
Chelation-promoted efficient C−H/N−H cross dehydrogenative coupling between picolinamides and simple ethers under copper catalysis Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-11 Qiang Yue, Zhen Xiao, Zhengkun Kuang, Zhengding Su, Qian Zhang, Dong Li
A highly efficient copper-catalyzed C−H/N−H cross dehydrogenative coupling between picolinamides and simple ethers was developed. The reaction was promoted by the chelation assistance of removable picolinyl group and exhibited excellent TON and TOF number. This method was applicable to both N−aryl and alkyl picolinamides as well as various cyclic and acyclic ethers with good functional group compatibility. It also possessed the merit of air and moisture tolerance and easy operation.
A Heteroarylamine Library: Indium-Catalyzed Nucleophilic Aromatic Substitution of Alkoxyheteroarenes with Amines Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-11 Kyohei Yonekura, Yasuhiro Yoshimura, Mizuri Akehi, Teruhisa Tsuchimoto
Under indium Lewis acid catalysis, electron-rich five-membered heteroaryl electrophiles fused with/without a benzene ring were found to couple with amines to produce heteroarylamines with broad structural diversity. The heteroarylamine formation proceeds through the cleavage of a heteroaryl–OMe bond by the nucleophilic attack of the amine based on the nucleophilic aromatic substitution (SNAr). In contrast to the corresponding traditional SNAr amination, the present SNAr-based heteroaryl amination can be performed without relying on both heteroaryl electrophiles with electron-withdrawing groups and nucleophilicity-enhanced metal amides. High compatibility towards the functional groups such as NO2, Br, I, CF3, CN, CO2Et, pyridyl, thiazolyl, C=C, and OH groups was observed, thus showing the practicality and reliability of this method. Mechanistic studies indicated that a carbon–indium bond is likely to be formed on the heteroaryl ring during the process.
Visible-Light-Promoted Decarboxylative Giese Reactions of α-Aryl Ethenylphosphonates and the Application in the Synthesis of Fosmidomycin Analogue Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-11 Ting Guo, Li Zhang, Yewen Fang, Xiaoping Jin, Yan Li, Ruifeng Li, Xie Li, Wu Cen, Xiaobo Liu, Zongming Tian
An unprecedented approach for the synthesis of α-aryl alkylphosphonates based on visible-light photocatalytic Giese reaction of α-aryl vinylphosphonates with aliphatic carboxylic acids has been successfully developed. This protocol tolerates a wide range of functional groups and shows broad substrate scope with regard to both the carboxylic acid and vinylphosphonate components. With sequential Giese/hydrolysis reactions as the strategy, the oxo-phosphonates could be easily accessible. The synthetic application of the hydroformylation reaction was demonstrated by the synthesis of the intermediate of α-phenyl substituted fosmidomycin analogue. Furthermore, the competitive decarboxylative alkylation of vinylphosphonate and acrylate was also investigated.
Water-Mediated One-pot Three-Component Synthesis of Hydrazinyl-Thiazoles Catalyzed by Copper Oxide Nanoparticles Dispersed on Titanium Dioxide Support: A Green Catalytic Process Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-06 Trivikram Reddy Gundala, Kumar Godugu, Nallagondu Chinna Gangi Reddy
The present work describes the catalytic activity of copper oxide nanoparticles dispersed on titanium dioxide in water for one-pot synthesis of a library of hydrazinyl-thiazoles via a three-component reaction of various aldehydes/ketones with thiosemicarbazide and different phenacyl bromides. The structure of the synthesized compound, (E)-4-(4-bromophenyl)-2-(2-(4-methoxybenzylidene) hydrazinyl)thiazole is confirmed by single crystal X-ray diffraction studies. The catalyst prepared by a molten-salt method is characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy and electron spin resonance spectroscopy. The noteworthy advantages of this method include its broad substrate scope, clean reaction profile, short reaction times and high yields at low catalyst loading. Further, the product does not require any chromatographic purification and the method has the potential for large-scale applications in pharmaceutical industries. In addition, the developed catalyst can be recovered and reused for 5 times without significant loss of activity. Mechanistic studies suggest that the reaction begins with the activation of the carbonyl group of both aldehyde/ketone and phenacyl bromide by copper oxide nanoparticles supported on titanium dioxide in water. These studies reveal that the reaction proceeds via the formation of thiosemicarbazone intermediate.
Rhodium(III)-Catalyzed Selective Direct Olefination of Imidazoles Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-06 Lijin Xu, Haoqiang Zhao, Jianbin Xu, Changjun Chen, Xin Xu, Yixiao Pan, Zongyao Zhang, Huanrong Li
Rhodium(III)-catalyzed chelation-assisted highly regio- and stereoselective direct olefination of imidazoles with olefins has been developed. A broad range of C2-substituted N-(2-pyrimidyl)imidazoles underwent smooth C5-olefination with both activated and unactivated olefins to furnish the corresponding products in good to excellent yields with high tolerance of functional groups on both coupling partners in the presence of a cationic rhodium(III) catalyst. The combination of a catalytic amount of Cu(OAc)2 (copper(II) acetate) and O2 (oxygen) serves as the terminal oxidant. This protocol strongly relies on the use of 2-substituted imidazoles as the substrates, and the presence of readily installable and removable pyrimidyl directing group was found to be critical for catalysis. Mechanistic studies suggest the involvement of a five-membered rhodacycle as the key intermediate in the catalytic cycle. The method can also be extended to the coupling reaction of benzimidazoles with olefins
Cobalt(III)–Catalyzed C–H Activation: A Secondary Amide Directed Decarboxylative Functionalization of Alkynyl Carboxylic Acids Wherein Amide NH–group Remains Unreactive Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-04 Nachimuthu Muniraj, Kandikere Prabhu
A Co(III)-catalyzed C-H activation reaction for ortho-alkenylation of benzamides (aryl/heteroaryl) and C2-alkenylation of indole derivatives have been developed using alkynyl carboxylic acid as an alkene source. A high regioselectivity has been achieved in the formation of disubstituted alkenes, and the possible cyclic products were not observed. This efficient alkenylation shows a broad range of substrate scope with a good functional group tolerance. The application of the methodology has been showcased by transforming an alkenylated amide to a 3-hydroxy isoindolinone derivative.
Synthesis of 7-Azaindole Amidated Derivatives: An Efficient Usage of Acyl Azides as the Nitrogen Source Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-03 Lin Dong, Wei-Huan Li, Chao Li
The dual behaviour of acyl azides in transition-metal-catalyzed direct C−H amidation is investigated. Variously substituted acyl azides reacted smoothly with 7-azaindoles providing a diversity of C−C or C−N amidated 7-azaindole derivatives. This amidation reaction shows an excellent controllability, which is believed to be dependent on catalyst system.
Metal-Free Azidation of α-Hydroxy Esters and α-Hydroxy Ketones Using Azidotrimethylsilane Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-03 Xiao-Ping Yin, Lei Zhu, Jian Zhou
We herein report a commercially available perchloric acid catalyst capable of catalyzing the azidation of α-hydroxy esters, α-hydroxy ketones and taddols using azidotrimethylsilane in dichloromethane at room temperature. Various substituted tertiary alcohols are well tolerated in this reaction. Cα-tetrasubstituted α-amino acid derivatives were prepared by one-pot sequential azidation and hydrogenation procedure. The advantage of this newly developed method includes operational simplicity, ready availability of catalyst, scale-up ability, and also good funcational group compatibility.
Regioselective C-7 Nitration of 8-Aminoquinoline Amides Using tert-Butyl Nitrite Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-03 Alakananda Hajra, Susmita Mondal, Sadhanendu Samanta
Regioselective C-7 nitration of 8-aminoquinoline amide has been achieved using tert-butyl nitrite under metal-free conditions at ambient temperature. The protocol is applicable to various aryl, heteroaryl as well as aliphatic carboxamides, and exhibits high functional group compatibility. The present method provides selective mononitrated quinoline derivatives. Experimental results suggest that the reaction likely proceeds through a radical pathway.
Regioselective Synthesis of Angular Isocoumarinoselenazoles: A Benzoselenazole Directed Site Specific Ruthenium-catalyzed C(sp2)-H Functionalization Adv. Synth. Catal. (IF 5.646) Pub Date : 2018-01-02 SANDIP DHOLE, Jen-Yu Liao, Sunil Kumar Dhull, Deepak Salunke, Chung-Ming Sun
Synthesis of new angular isocoumarinoselenazoles is described which involves the construction of 2-amino benzoselenazoles, their regioselective C2 N-alkylation and alkyne insertion. An expeditious and metal-free synthesis of 2-aminobenzoselenazoles by the reaction of methyl 3-amino-4-fluorobenzoate and isoselenocyanates was achieved. Further N-alkylation of 2-aminobenzoselenazoles resulted the formation of two regioisomers with differential reactivity towards alkyne insertion. The regioselective construction of α-pyrone ring on the benzo[1,3-d]selenazole skeleton was achieved via ruthenium (II)-catalyzed oxidative annulation. It is clear that the selenazole nitrogen plays an important role for the observed selectivity.
Rhodium-Catalyzed Regioselective Ortho C-H Olefination of 2-Arylindoles via NH-Indole-Directed C-H Bond Cleavage Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-31 Qingshuai Han, Xiemin Guo, Ziyuan Tang, Lv Su, Zizhu Yao, Xiaofeng Zhang, Shen Lin, ShengChang Xiang, Qiufeng Huang
In the past decades, C-H oxidative olefination of indole at C-2, C-3, C-4 and C-7 positions was well addressed. We report here a rhodium-catalyzed NH-indole-directed ortho C-H bond olefination of 2-arylindoles. This cross-dehydrogenative-coupling proved to be broad in substrate scope, tolerating a variety of functional groups. The synthesis of 6H-isoindolo[2,1-α]indoles via rhodium-catalyzed ortho C-H olefination and subsequent intramolecular aza-Michael reaction of 2-arylindoles was also demonstrated.
Direct Reductive Amination of Carbonyl Compounds Catalyzed by a Moisture Tolerant Tin(IV) Lewis Acid Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-28 Joshua Sapsford, Daniel Scott, Nathan Allcock, Matthew J. Fuchter, Christopher Tighe, Andrew Ashley
Despite the ever-broadening applications of main-group ‘frustrated Lewis pair’ (FLP) chemistry to both new and established reactions, their typical intolerance of water, especially at elevated temperatures (> 100°C), represents a key barrier to their mainstream adoption. Herein we report that FLPs based on the Lewis acid iPr3SnOTf are moisture tolerant in the presence of moderately strong nitrogenous bases, even under high temperature regimes, allowing them to operate as simple and effective catalysts for the reductive amination of organic carbonyls, including for challenging bulky amine and carbonyl substrate partners.
Rh-Catalyzed Annulation of ortho- C-H Bonds of 2-Arylimidazoles with 1,4,2-Dioxazol-5-ones toward 5-Arylimidazo[1,2-c]quinazolines Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-28 Xiaopeng Wu, Song Sun, Shengbo Xu, Jiang Cheng
A Rh-catalyzed unique and direct approach for constructing a series of 5-arylimidazo[1,2-c]quinazolines in moderate to excellent yields from simple and readily available 2-arylimidazoles and 3-phenyl-1,4,2-dioxazol-5-ones was described. This procedure proceeds with sequential ortho- C-H bond amidation and cyclization, which represents a facile and straightforward pathway to access such frameworks.
Copper-Catalyzed Stereoselective Defluorinative Borylation and Silylation of gem-Difluoroalkenes Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-26 Dong-Hang Tan, E Lin, Wei-Wei Ji, Yao-Fu Zeng, Wen-Xin Fan, Qingjiang Li, Hui Gao, Honggen Wang
The copper-catalyzed stereoselective defluorinative borylation and silylation of gem-difluoroalkenes was developed. The protocol led to the exclusive formation of Z type monofluoroalkenyl borons and silanes in generally good efficiency with broad substrate scope. The products formed could be readily transformed to other F-containing molecules by taking advantage of the versatile reactivities of C-B and C-Si bonds. Experimental and theoretical mechanistic studies were conducted which support an olefin insertion/syn-planar β-F elimination pathway.
Visible Light-Induced Synthetic Approach for Selenylative Spirocyclization of N-Aryl Alkynamides with Molecular Oxygen as Oxidant Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-26 Harekrishna Sahoo, Anup Mandal, Suman Dana, Mahiuddin Baidya
A visible light-induced (blue LED) radical cascade has been devised to effect selenylative spirocyclization of N-aryl alkynamides at room temperature under oxygen atmosphere and without the aid of external photocatalyst. The protocol is operationally simple, scalable, and offers clean synthesis of 3-selenospiro[4,5]trienones in high yields (up to 92%). A novel spiro-ring-opening strategy has also been accomplished to access fully substituted acryl amides.
Organocatalytic Synthesis of Oxazolines and Dihydrooxazines from Allyl-Amides: Bypassing the Inherent Regioselectivity of the Cyclization Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-25 Alexis Theodorou, Ierasia Triandafillidi, Christoforos Kokotos
A selective and efficient methodology for the construction of either oxazolines or dihydrooxazines from the corresponding allyl-amides is reported. Bypassing the inherent selectivity of the cyclization and depending on the substitution pattern of the substrate, a selective epoxidation-cyclization was developed leading to either the five-membered or the six-membered ring, upon simple and complementary reaction conditions. The cyclization products were obtained in good to excellent yields and high selectivities.
Construction of Vicinal Tetrasubstituted Stereogenic Centers via a Mannich-Type Organocatalyzed Addition of Δ2-Pyrrolin-4-ones to Isatine Imines Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-25 Sebastijan Ričko, Anže Meden, Luka Ciber, Bogdan Štefane, Franc Pozgan, Jurij Svete, Uroš Grošelj
Racemic Δ2-pyrrolin-4-ones (i.e. 4-pyrrolones), easily available in two steps from N-protected α-amino acids, undergo organocatalysed asymmetric Mannich-type addition to isatin-derived ketimines to furnish the non-racemic oxindole–Δ2-pyrrolin-4-one adducts, stereoselectively (up to 96% ee, dr ≥15:1). The oxindole–pyrrolone products feature vicinal tetrasubstituted carbon stereocenters. The developed protocol has a broad substrate scope and tolerates diverse substituents at position C-5 in 4-pyrrolones and at positions N-1 and C-5/7 in isatin-imines.
Diastereoselective Electrophilic Trifluoromethylthiolation of Chiral Oxazolidinones: Access to Enantiopure α-SCF3 Alcohols Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-25 Hélène Chachignon, Evgenii Kondrashov, Dominique Cahard
Lithium imide enolates featuring Evans’ chiral oxazolidinone auxiliary were involved in diastereoselective α-trifluoromethylthiolation with electrophilic SCF3 donors. Diastereopure products were isolated and converted to enantiopure α-SCF3 alcohols without racemisation.
Palladium-catalyzed Selective Amination of Aryl(haloaryl)amines with 9H-Carbazole Derivatives Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-25 Yuhki Otsuka, tetsuya yamamoto, Takanori Miyazaki, Tetsu Yamakawa
Palladium-catalyzed amination of aryl(haloaryl)amines with 9H-carbazole derivatives was investigated. In the amination of (4-bromophenyl)phenylamine with 9H-carbazole by the use of Pd2(dba)3/PtBu3/NaOtBu catalyst, the main product was desired 9-[4-(phenylamino)phenyl]-9H-carbazole in 60% yield with conversion of (4-bromophenyl)phenylamine >99%, and the concomitant formation of 9-[4-[phenyl[4-(phenylamino)phenyl]amino]phenyl]-9H-carbazole (15% yield), which is the consecutive by-product, was observed. When XPhos was used instead of PtBu3, the desired product was provided in 81% yield and the consecutive by-product was suppressed to 7.7%. The yield of the desired product reached 98% by the use of tBu-XPhos. Such excellent yields of the desired product were also obtained with other 2-di- tert-butyl- or 2-di(1-adamantyl)phosphino-1,1’-biaryls. Various 9-(arylamino)aryl-9H-carbazoles could be synthesized from aryl(haloaryl)amines and 9H-carbazole derivatives in high yields by the use of tBu-XPhos. The amination of 4-bromotoluene with a mixture of diphenylamine and 9H-carbazole gave only 9-o-tolyl-9H-carbazole with tBu-XPhos, while the use of PtBu3 or XPhos afforded the mixture of 9-o-tolyl-9H-carbazole and diphenyl(o-tolyl)amine, indicating that Pd2(dba)3/tBu-XPhos/NaOtBu catalyst high selectively favors 9H-carbazole over diphenylamine as an amination substrate.
Pyrroline Synthesis via Visible-Light-Promoted Hydroimination of Unactivated Alkenes with N,N'-Dimethylpropyleneurea as H-Donor Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-25 Sai-Hu Cai, Ding-Xing Wang, Lu Ye, Ze-Yao Liu, Chao Feng, Teck-Peng Loh
Synthesis of 3,4-pyrroline derivatives via visible-light-induced hydro/oxyimination of unactivated oleﬁns is reported. In the presence of the photoredox catalyst fac-Ir(ppy)3, the key iminyl radical intermediate can be readily generated from O-acyl oximes, and undergoes intramolecular cyclization and H-abstraction from solvent or is trapped by TEMPO to give the corresponding hydro/oxyimination product, respectively. Mechanistic investigations indicate that N,N'-dimethylpropylene urea (DMPU) works as both reducing agent for catalyst regeneration and H-donor for product formation in this process.
Enantioselective Conjugate Addition of 2-Acylimidazoles with Nitroalkenes Promoted by Chiral-at-Metal Rhodium(III) Complexes Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-25 Ganesh Kumar Thota, Gui-Jun Sun, Tao Deng, Yi Li, Qiang Kang
An enantioselective conjugate addition of 2-acyl imidazoles with nitro-alkenes catalyzed by chiral-at-metal Rh(III) complex under mild reaction conditions was developed, affording versatile γ-nitro-ketone skeletons in good yields with excellent enantioselectivities (up to >99% ee).
N-Arylated Sulfoximines as Cross-Coupling Building Blocks Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-24 Anne-Katrin Bachon, Anne-Dorothee Steinkamp, Carsten Bolm
The application of borylated N-aryl sulfoximines as newly designed synthetic building blocks in Suzuki-type cross coupling reactions offers rapid access to a wide range of N-biaryl derivatives with potential relevance for medicinal chemistry and crop protection in good to excellent yields (up to 98%).
Mild Ring Contractions of Cyclobutanols to Cyclopropyl Ketones via Hypervalent Iodine Oxidation Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-24 Yan Sun, Xin Huang, Xiaojin Li, Fan Luo, Lei Zhang, Mengyuan Chen, Shiya Zheng, Bo Peng
An iodine-mediated oxidative ring contraction of cyclobutanols has been developed. The reaction allows the synthesis of a wide range of aryl cyclopropyl ketones under mild and eco-friendly conditions. A variety of functional groups including aromatic or alkyl halides, ethers, esters, ketones, alkenes, and even aldehydes are nicely tolerated in the reaction. This is in contrast with traditional synthetic approaches for which poor functional group tolerance is often a problem. The practicality of the method is also highlighted by the tunability of iodine oxidation system. Specifically, combining the iodine(III) reagent with an appropriate base allows the reaction to accommodate a range of challenging electron-rich arene substrates. The facile scalability of this reaction is also exhibited herein.
Base-Promoted Tandem Cyclization for the Synthesis of Benzonitriles by C–C Bond Construction Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-24 Cheng-Zhi Zhu, Yin Wei, Min Shi
A facile synthesis of benzonitriles via base-promoted tandem cyclization reaction of α,β-unsaturated enones having electron-withdrawing group (EWG) and 2-acyl-acrylonitriles has been developed. This new synthetic method to access benzonitriles is suitable for a wide range of substrates. A plausible reaction mechanism has been proposed on the basis of previous literature and our own investigations.
Oxidative Catalytic Spiroketalization Leading to Diastereoselective Spiro[benzofuran-2,1'-isochromene]s Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-24 Jiang-Kai Qiu, Wen-Juan Hao, Guigen Li, Bo Jiang
A new one-pot, two-step Ag-catalyzed spiroketalization of the in-situ generated quinone imine ketals (QIKs) with β-alkynyl ketones has been established, enabling multiple C−O and C−C bond-forming reactions to access densely functionalized spiro[benzofuran-2,1'-isochromene] derivatives with generally good yields. The use of β-alkynyl ketones bearing alkyl and aryl groups located at α-position of the carbonyl group could lead to highly diastereoselective spiro[chromane-2,1’-isochromene] derivatives. The reaction features broad substrate scope, mild oxidative catalytic conditions and excellent diastereoselectivity.
Synthesis of 2-(alpha,alpha,alpha-Trifluoromethyl)-dibenzopyranones with Rhodium(III)-catalyzed Formal anti-Michael Addition as Key Step Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-24 Ling Pan, Jinhuan Dong, Di Xie, Yifei Li, QUN LIU
A novel rhodium(III)-catalyzed synthesis of 2-(alpha,alpha,alpha-trifluoromethyl)-dibenzopyranones from easily available 4-(alpha,alpha,alpha-trifluoromethyl)-p-quinols and N-methoxyarylamides is described. Rhodium(III)-catalyzed formal anti-Michael addition was proposed to be a crucial step in this [3 + 3] annulation with N-methoxyarylamides as effective 1,3-dipoles, providing a concise and efficient approach for the construction of alpha,alpha,alpha-trifluoromethyl-containing dibenzopyranones under mild reaction conditions.
Efficient Synthesis of Amines by Iron-Catalyzed C=N Transfer Hydrogenation and C=O Reductive Amination Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-17 Umberto Piarulli, Sofia Vailati-Facchini, Mattia Cettolin, Xishan Bai, Giuseppe Casamassima, Luca Pignataro, Cesare Gennari
Here we report the catalytic transfer hydrogenation (CTH) of non-activated imines promoted by a Fe-catalyst in the absence of Lewis acid co-catalysts. Use of the (cyclopentadienone)iron complex 1, which is much more active than the classical ‘Knölker complex’ 2, allowed to reduce a number of N-aryl and N-alkyl imines in very good yields using iPrOH as hydrogen source. The reaction proceeds with relatively low catalyst loading (0.5-2 mol%) and, remarkably, its scope includes also ketimines, whose reduction with a Fe-complex as the only catalyst has little precedents. Based on this methodology, we developed a one-pot CTH protocol for the reductive amination of aldehydes/ketones, which provides access to secondary amines in high yield without the need to isolate imine intermediates.
Synthesis of Sulfonated 5-Aminopyrazoles by I2/Benzoyl Peroxide-Mediated Tandem Reaction Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-16 Dongping Cheng, tianpeng chen, xiaoliang xu, jizhong yan
The tandem reaction of 3-morpholinoacrylonitrile with sulfonyl hydrazides mediated by I2/benzoyl peroxide (BPO) is reported, which offers an efficient approach for the synthesis of sulfonated 5-aminopyrazoles. It can bear a large scope of the substrates, and be used for the synthesis of aromatic, heteroaromatic and aliphatic sulfonated 5-aminopyrazoles.
Nondirecting Group sp3 C−H Activation for Synthesis of Bibenzyls via Homo-coupling as Catalyzed by Reduced Graphene Oxide Supported PtPd@Pt Porous Nanospheres Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-16 Zheng-Jun Wang, Jing-Jing Lv, Rong-Nan Yi, Min Xiao, Jiu-Ju Feng, Zhiwu Liang, Ai-Jun Wang, Xinhua Xu
The use of heterogeneous bimetallic Pd-based nanocatalyst for directing the inactivated sp3 C−H coupling has been scarcely explored. This work reported the formation of symmetrical C−C bonds from the inactivated sp3 C−H bonds catalyzed by employing reduced graphene oxide supported PtPd@Pt porous nanospheres. The reaction of sp3 C−H activation proceeded under mild conditions without any solvent, ligand or directing group. It is a higher atom-, step- and cost-effectiveness strategy for developing heterogeneous catalysts in the synthesis of bibenzyls with various functional groups (e.g. aryl, alkyl, methoxyl, halogen, ester, and pyridyl).
Synthesis of Chiral Sulfonyl Lactones via Copper-Catalyzed Asymmetric Radical Reaction of DABCO·(SO2) Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-16 Yang Wang, Lingling Deng, Jie Zhou, Xiaochen Wang, Haibo Mei, Jianlin Han, Yi Pan
In the present work, an asymmetric copper-catalyzed radical multi-component cascade reaction of an unsaturated carboxylic acid, aryldiazonium tetrafluoroborate, and DABCO·(SO2)2 (DABSO) has been developed for the enantioselective synthesis of sulfonyl lactones. In this reaction, this SO2 surrogate, DABSO was applied for the first time in the construction of chiral compounds. This multiple-step asymmetric radical reaction was carried out under mild conditions and tolerated a wide range of substrates, resulting in the corresponding sulfonyl lactones with up to 95% chemical yields and 88% ee. The current reaction enriches the research contents of DABSO, and provides a new and efficient strategy to chiral functionalized lactones bearing quarternary stereogenic center.
Substituted Hantzsch Esters as Versatile Radical Reservoirs in Photoredox Reactions Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-15 Fangjun Gu, Wenhao Huang, Xu Liu, Wen-Xin Chen, Xu Cheng
Abstract. Substituted Hantzsch esters can act as radical reservoirs in photoredox reactions, steadily releasing a carbon radical and a hydrogen atom radical in the absence of an additional electron acceptor. We propose that radical release by substituted Hantzsch esters occurs via a mechanism involving an internal redox cycle. Cinnamidecinnamides, styrenes, a,b-unsaturated acids, and diarylethenes could be alkylated smoothly with these reagents.
Transition-Metal-Free Regioselective Alkylation of Quinoline N-Oxides via Oxidative Alkyl Migration and C-C Bond Cleavage of tert-/sec- Alcohols Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-14 Subhash Ghosh, Chiranjit Sen
An unprecedented C2-alkylation of quinoline N-oxide derivatives via C-C bond activation of tert- and sec-alkyl alcohol is described using hypervalent iodine (III) reagent PhI(OAc)2 (PIDA). This regioselective alkylation using mild hypervalent iodine reagents is more practical, operationally simple and transition metal free. The reaction proceeds efficiently with a broad range of substrates including quinoline, isoquinoline, and pyridine N-oxides using a variety of tert-/sec- alcohols. From experimental outcome, we also propose a rationalized mechanism, mediated by PIDA.
Design of C3-Alkenyl-Substituted 2-Indolylmethanols for Catalytic Asymmetric Interrupted Nazarov-Type Cyclization Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-13 Cong-Shuai Wang, Jia-Le Wu, Can Li, Lin-Zhi Li, Guang-Jian Mei, Feng Shi
The C3-alkenyl-substituted 2-indolylmethanols have been designed as a new class of substrates for catalytic asymmetric interrupted Nazarov-type cyclizations. In the presence of chiral phosphoric acid as a mild chiral Brønsted acid, the interrupted Nazarov-type cyclization of C3-alkenyl-substituted 2-indolylmethanols with nucleophiles occurred smoothly to construct cyclopenta[b]indole frameworks in generally excellent diastereo- and enantioselectivities (up to >95:5 dr, >99% ee).
Pd/Mn Bimetallic Relay Catalysis for Aerobic Aldoxime Dehydration to Nitriles Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-13 Dongliang Zhang, Yaping Huang, Erlei Zhang, Rong Yi, Chao Chen, Lei Yu, Qing XU
A Pd/Mn bimetal system was found to be an effective catalyst for dehydration of aldoximes to the useful nitriles under mild aerobic conditions. Different to the known metal-catalyzed aldoxime dehydration reactions, this reaction very possibly proceeded via an alternative mechanism of Pd/Mn bimetal relay catalysis involving a Mn-catalyzed aerobic oxidation of aldoximes to nitrile oxides by air and a Pd-catalyzed oxygen transfer from the nitrile oxides to the solvent acetonitrile. This method tolerates a variety of substrates including sterically bulky ones and also the natural product derivative.
Catalytic Enantioselective Povarov Reactions of Ferrocenecarbaldehyde-Derived Imines – Brønsted Acid Catalysis at Parts-Per-Million Level Loading Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-12 Dragana Stevanovic, Giulio Bertuzzi, Andrea Mazzanti, Mariafrancesca Fochi, Luca Bernardi
Despite the broad interest in ferrocene containing compounds, ferrocenyl substrates have been employed in catalytic asymmetric settings only sporadically. Herein, catalytic asymmetric Povarov reactions with ferrocenecarbaldehyde-derived N-aryl imines are presented. This study demonstrates that the stereoelectronic properties of ferrocenyl imines do not preclude their engagement in enantioselective phosphoric acid catalysis: cycloadducts derived from benzyl N-vinylcarbamate were obtained in good yields and nearly enantiopure form using 0.1 mol% of a standard Brønsted acid catalyst. Furthermore, it is shown that specific optimisation with some substrates allowed to lower the catalyst loading up to 10-20 parts-per-million, an unprecedented value for phosphoric acid catalysts. Such low loading protocol could be applied to a preparative scale reaction, and to imines derived from arylaldehydes.
Merging Brønsted Acid and Hydrogen-Bonding Catalysis: Metal-Free Dearomatization of Phenols via ipso-Friedel-Crafts Alkylation to Produce Functionalized Spirolactams Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-08 Shingo Harada, Irene Kwok, Hiroki Nakayama, Ayaka Kanda, Tetsuhiro Nemoto
Intramolecular dearomative cyclization of phenols with α-diazoamide units for synthesizing functionalized spirolactams was developed by merging Brønsted acid and hydrogen-bonding catalysis as an advantageous alternative to transition metal catalysis. This metal carbenoid-free strategy enables high chemoselectivity by suppressing potentially competing C–H insertion reactions and a Büchner reaction. Preliminary mechanistic studies were performed to elucidate the positive effect of the combined use of the catalysts, and extension to an asymmetric reaction was achieved.
Synthesis of Sulfonated Benzo[d][1,3]oxazines by Merging Photoredox Catalysis and Insertion of Sulfur Dioxide Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-08 Tong Liu, Danqing Zheng, Zhenhua Li, Jie Wu
A photocatalytic reaction of N-(2-vinylphenyl)amides, DABCO•(SO2)2 and aryldiazonium tetrafluoroborates for the synthesis of 4-((arylsulfonyl)methyl)-4H-benzo[d][1,3]oxazines under mild conditions is reported. This synthetic approach is enabled by merging photoredox catalysis and insertion of sulfur dioxide via radical process. The specific role of photoredox catalysis in this transformation is supported by mechanistic investigation and theoretical calculations.
Brønsted Acid-Mediated Formal [3+3] Annulation Between Propargylic Alcohols and 1,3-Diketones Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-08 Ya-Ping Han, Xue-Song Li, Xin-Yu Zhu, Zhou Sun, Ming Li, Yu-Zhao Wang, Yong-Min Liang
A Brønsted acid-mediated formal [3+3] cascade annulation of propargylic alcohols with 1,3-diketones proceeds through a sequential Meyer−Schuster rearrangement/1,2-addition. This protocol, which has a wide scope and is conducted under an ambient atmosphere, enables access to a broad array of valuable chromenone derivatives related to many natural products in satisfactory yields under mild conditions. This method could be scaled up to the gram scale, which highlights the latent applicability of this transformation.
Visible-Light-Promoted Alkylation of Indoles with Tertiary Amines by the Oxidation of a sp3 C-H Bond Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-08 Xuan Ding, Chun-Lin Dong, Zhi Guan, Yan-Hong He
A visible-light driven reaction for the synthesis of 3-arylmethyl indole derivatives using tertiary amines and indoles was first reported. Corresponding products were obtained with yields of up to 70%, and various functional groups on the indoles were well tolerated when Rose Bengal was used as a photosensitizer and air was used as a green oxidant under mild reaction conditions.
One-Pot Synthesis of 2,3,5-Trisubstituted Thiophenes through Three-Component Assembly of Arylacetaldehydes, Elemental Sulfur, and 1,3-Dicarbonyls Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-08 Huawen Huang, Zilong Wang, Zhonghua Qu, Fuhong Xiao, Guojun Deng
The three-component reaction for the synthesis of 2-arylthiophenes has been developed. Easily available arylacetaldehydes, 1,3-dicarbonyls, and elemental sulfur were directly assembled through cascade condensation/ annulation under base conditions. The present protocol provides a facile entry to 2,3,5-trisubstituted thiophenes in moderate to excellent yields with good functional group tolerance.
Hypervalent Iodine-Mediated Alkene Functionalization: Oxazoline and Thiazoline Synthesis via Inter-/Intramolecular Aminohydroxylation and Thioamination Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-09 Hyeonho Jeon, Da Rong Kim, Ji Hoon Lee, Jaeyoung Song, Won Seok Lee, Dong Wook Kang, Soosung Kang, Seok Beom Lee, Sungwook Choi, Ki Bum Hong
A metal-free oxidative difunctionalization of N-allylamides and N-allylthioamides has been developed. This system features the use of a hypervalent iodine oxidant with electron-deficient amines to access 5-amino-oxazoline and thiazoline scaffolds under mild conditions. Notably, various electron-deficient amines were systematically evaluated and we verified the reaction profile was originated from an attached (benzene)sulfonyl group.
Merging Gold Catalysis and Brønsted Acid Catalysis for the Synthesis of Tetrahydrobenzo[b][1,8]naphthyridines Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-10 Ruxia Yi, Xincheng Li, Boshun Wan
A gold(I)/Brønsted acid-catalyzed cyclization of 2-azidobenzaldehydes with 3-aza-1,6-enynes has been developed for the synthesis of tetrahydrobenzo[b][1,8]naphthyridine derivatives. This protocol enabled the modular synthesis of tetracyclic heterocycles in one operation with water and nitrogen gas as the byproducts.
Conversion of γ- and δ-Keto Esters into Optically Active Lactams. Transaminases in Cascade Processes Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-10 Ángela Mourelle-Insua, Luiz Arthur Zampieri, Iván Lavandera, Vicente Gotor-Fernández
A one-pot two-step enzymatic strategy has been designed for the production of optically active gamma- and delta-lactams in aqueous medium under mild conditions. The approach is based on the biotransamination of ethyl or methyl keto esters bearing different alkyl or aryl substitution patterns at alpha-position to the ketone functionality. In this manner, the keto esters were transformed into the corresponding amino esters with excellent conversions, which underwent spontaneous cyclisation in the reaction medium without addition of external reagents. Depending on the transaminase selectivity, both lactam enantiomers can be obtained, so initial enzyme screenings were performed using commercially available and made in house enzymes. Reaction conditions were optimised focusing on the substrate concentration, temperature and ratio of amine donor vs acceptor. Thus, ten gamma- and delta-lactams were obtained in good to high isolated yields (70-90%) and excellent selectivities (94-99%) after one or two days at 30 or 45 ºC.
Application of Homophthalic Anhydrides as 2C Building Blocks in Catalytic Asymmetric Cyclizations of ortho-Quinone Methides: Diastereo- and Enantioselective Construction of Dihydrocoumarin Frameworks Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-10 Ting Zhang, Chun Ma, Jia-Yu Zhou, Guang-Jian Mei, Feng Shi
A catalytic asymmetric [4+2] cyclization of ortho-quinone methides with homophthalic anhydrides in the presence of chiral squaramide-tertiary amine has been established. This method provides dihydrocoumarin frameworks in excellent diastereoselectivities (all >95:5 dr) and high enantioselectivities (81%-98% ee). This reaction represents the first application of homophthalic anhydrides as 2C building blocks in catalytic asymmetric cyclizations. In addition, this approach not only provides a useful method for constructing enantioenriched dihydrocoumarin frameworks but also advances the chemistry of catalytic asymmetric cyclizations of ortho-quinone methides.
An efficient synthesis of 6-oxa-spiro[3.4]octan-1-one derivates through 3-diazochroman-4-one and alkene Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-10 Meiling Xiao, Fuming Zhang, Zhe Du, Bao-chun Ma
Abstract: Spiro[2, 2-dimethyl-benzofuran, bicycle [4.2.0]octane]-7’-one with fused and spiro cyclic oxygen-containing rigid skeleton structure is obtained via Wolff rearrangement and cycloaddition with good yields. Then spiro[2, 2-dimethyl-benzofuran, hexahydro-isobenzofuran-2’-one] is synthesized by further Baeyer-Villiger oxidation. These two kinds of products have a special fused and spirocyclic oxygen-containing rigid skeleton structure and are reported by our group.
Asymmetric Amination of α-Chiral Aliphatic Aldehydes via Dynamic Kinetic Resolution to Access Stereocomplementary Brivaracetam and Pregabalin Precursors Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-10 Christine Fuchs, Judith Farnberger, Georg Steinkellner, Johann Sattler, Mathias Pickl, Robert Simon, Ferdinand Zepeck, Karl Gruber, Wolfgang Kroutil
Over the last decades biocatalysis has emerged as an indispensable and versatile tool for the asymmetric synthesis of active pharmaceutical ingredients (APIs). In this context, especially transaminases (TAs) have been successfully used for the preparation of numerous α-chiral, optically pure amines, serving as important building blocks for APIs. Here we elaborate on the development of transaminases recognizing the α-chiral centre adjacent to an aldehyde moiety with aliphatic residues, opening up concepts for novel synthetic routes to the antiepileptic drugs Brivaracetam and Pregabalin. The transformation proceeded via dynamic kinetic resolution (DKR) based on the bio-induced racemisation of the aldehyde enantiomers, enabling the amination of the racemic substrates with quantitative conversions. Medium, substrate as well as enzyme engineering gave access to both (R)- and (S)-enantiomers of the amine precursors of the stereocomplementary drugs in high optical purity, representing a short route to mentioned APIs.
Oxidant-Mediated Nitrogenation and Recyclization of Imidazo[1,2-a]pyridines with Sodium Azide: Synthesis of 4H-Pyrido[1,2-a][1,3,5]triazin-4-ones Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-11 Gangjian Cao, Zhengkai Chen, Jinyu Song, Jianfeng Xu, Maozhong Miao, Hongjun Ren
An expeditious and straightforward approach for the synthesis of 4H-pyrido[1,2-a][1,3,5]triazin-4-ones starting from readily available imidazo[1,2-a]pyridines and sodium azide has been presented under aerobic oxidative conditions. The reaction proceeded well with the promotion of potassium persulfate/potassium permanganate with good functional group tolerance. A wide range of biologically valuable 4H-pyrido[1,2-a][1,3,5]triazin-4-one scaffolds were assembled by this methodology. The gram-scale reaction was also achieved. A cascade nitrogenation and oxidative recyclization sequence could be involved in the reaction.
Ruthenium(II)-NNN-Pincer-Complex-Catalyzed Reactions Between Various Alcohols and Amines for Sustainable C-N and C-C Bond Formation Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-07 Milan Maji, Kaushik Chakrabarti, Bhaskar Paul, Bivas Chandra Roy, Sabuj Kundu
An air and moisture stable 2-hydroxypyridine based bifunctional ruthenium NNN-pincer complex catalyzed efficient (TON = 42840) N-alkylation of amines under mild conditions is described. Surprisingly, with cyclic secondary amines this methodology selectively produced only amides. Notably, N-methylation of several amines was achieved using methanol as a green methylating agent. Furthermore, with lower catalyst loading (0.2 mol%) and shorter reaction time (6 h) numerous substituted quinolines were synthesized from 2-aminobenzyl alcohols and secondary alcohols. The effectiveness of this protocol was further extended by successfully synthesizing 2-alkylaminoquinolines in one-pot fashion from amino alcohol, aliphatic nitriles and alcohols. Gram scale synthesis of various compounds was also investigated to demonstrate the synthetic applicability of this methodology.
Iridium-Catalyzed Dynamic Kinetic Stereoselective Allylic Etherification of Achmatowicz Rearrangement Products Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-07 Zhongpeng Zhu, Haoyuan Wang, CHRISTOPHER SIMMONS, Po-Sen Tseng, Xiang Qiu, Yu Zhang, XIYAN DUAN, Jing-Kui Yang, Weiping Tang
We recently developed a novel Ir-catalyzed dynamic kinetic isomerization reaction for Achmatowicz rearrangement products. In this update, we show that products derived from the Achmatowicz rearrangement can also undergo Ir-catalyzed dynamic kinetic allylic etherification in the presence of an appropriate ligand and additive to afford useful intermediates for the synthesis of carbohydrates. The addition of triphenyl phosphite ligand shuts down the isomerization pathway and promotes the allylic etherification pathway. The addition of diphenyl phosphate improved the diastereoselectivity for the addition reaction. Interestingly, opposite diastereoselectivity was observed for sterically demanding alcohol nucleophiles compared to less sterically demanding alcohol nucleophiles. The method was also applied to the synthesis of several 2,3-dideoxypyranosides.
Cyclopropanation of Benzene Rings by Oxidatively Generated α-Oxo Gold Carbene: One-Pot Access to Tetrahydropyranone-Fused Cycloheptatrienes from Propargyl Benzyl Ethers Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-07 Kegong Ji, Liming Zhang
[5+3] Cycloaddition of Zwitterionic Allylpalladium Intermediates with Azomethine Imines for Construction of N,O-Containing Eight-Membered Heterocycles Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-06 Hongchao GUO, Chunhao Yuan, Yang Wu, Dongqi Wang, Zhenhua Zhang, Chang Wang, Leijie Zhou, Cheng Zhang, Baoan Song
A [5+3] cycloaddition of zwitterionic allylpalladium intermediates with 1,3-dipoles is developed, providing N,O-containing eight-membered heterocyclic compounds in high yields. Catalytically generated zwitterionic allylpalladium intermediates in situ from vinylethylene carbonates or vinyloxiranes acted as dipolarophile.
Redox active sodium iodide / recyclable heterogeneous solid acid: An efficient dual catalytic system for electrochemically oxidative α-C-H thiocyanation and sulfenylation of ketones Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-06 Sen Liang, Cheng-Chu Zeng, Hongyu Tian, baoguo sun, xugang luo, fazheng ren
An efficient electrochemically oxidative α-C-H thiocyanation and sulfenylation of ketones has been developed in a simple undivided cell under constant current condition. The electrochemistry performs using NaI as the redox catalyst and heterogeneous solid salt Amberlyst-15(H)® (A-15(H)) as proton catalyst without the addition of external conductive salts. The protocol proved to be practical since the solid salt could be reused in up to five consecutive gram-scale runs without significant decrease in efficiency. Control experiments and cyclic voltammetry analysis disclose that the reaction proceeds likely via a cascade α-halogenation and subsequent thiocyanation or sulfenylation.
An Allene Approach to Tetrahydrofuran-Fused Bicyclo[2.2.2]oct-2-enes Adv. Synth. Catal. (IF 5.646) Pub Date : 2017-12-06 Shihua Song, Chunling Fu, Xin Huang, Shengming Ma
An efficient access to tetrahydrofuran-fused bicyclo[2.2.2]oct-2-enes via palladium-catalyzed cyclization of oxygen-tethered 2,7-alkadiynylic carbonates with 2-(buta-2,3-dienyl)malononitrile has been developed. Perfect chiral induction was observed when a substituent was introduced to the propargylic position affording the optically active polycyclic products of both enantiomers. Control experiments showed that the oxygen tether of 2,7-alkadiynylic carbonates and the two cyano groups in allene 2a are indispensible for this transformation.
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