(2019). Melamine-(H2SO4)3/Melamine-(HNO3)3 Instead of H2SO4/HNO3: Benign System for Oxidation/Nitration Reactions from in situ NO2+. Organic Preparations and Procedures International: Vol. 51, No. 6, pp. 589-594.

In this work the patent landscape of catalytic hydrogenation reactions was evaluated with the aid of the online database Patbase®. The respective classifications were used to distinguish the development of trends among patents. The findings give a detailed picture of the patent activity on the field of hydrogenation catalysis and may give the user information on technological areas that occur more often in the patent literature than others.

Compared with biocatalysis in aqueous media, the use of enzymes in neat organic solvents enables increased solubility of hydrophobic substrates and can lead to more favorable thermodynamic equilibria, avoidance of possible hydrolytic side reactions and easier product recovery. ω‐Transaminases from Arthrobacter sp. (AsR‐ωTA) and Chromobacterium violaceum (Cv‐ωTA) were immobilized on controlled porosity glass metal‐ion affinity beads (EziG) and applied in neat organic solvents for the amination of 1‐phenoxypropan‐2‐one with 2‐propylamine. The reaction system was investigated in terms of type of carrier material, organic solvents and reaction temperature. Optimal conditions were found with more hydrophobic carrier materials and toluene as reaction solvent. The system’s water activity (αw) was controlled via salt hydrate pairs during both the biocatalyst immobilization step and the progress of the reaction in different non‐polar solvents. Notably, the two immobilized ωTAs displayed different optimal values of αw, namely 0.7 for EziG3‐AsR‐ωTA and 0.2 for EziG3‐Cv‐ωTA. In general, high catalytic activity was observed in various organic solvents even when a high substrate concentration (450‐550 mM) and only one equivalent of 2‐propylamine were applied. Under batch conditions, a chemical turnover (TTN) above 13000 was obtained over four subsequent reaction cycles with the same batch of EziG‐immobilized ωTA. Finally, the applicability of the immobilized biocatalyst in neat organic solvents was further demonstrated in a continuous flow packed‐bed reactor. The flow reactor showed excellent performance without observable loss of enzymatic catalytic activity over several days of operation. In general, ca. 70% conversion was obtained in 72 hours using a 1.82 mL flow reactor and toluene as flow solvent, thus affording a space‐time yield of 1.99 g L‐1 h‐1. Conversion reached above 90% when the reaction was run up to 120 hours.

Tandem catalysis, the use of a single catalyst to promote two or more mechanistically distinct cycles in one pot to assemble complex organic molecules, is an attractive target. In this paper, we report a reductant‐triggered tandem palladium catalysis process that rapidly assembles 3,4‐fused tricyclic indoles from three readily available starting materials. This tandem process involves a Pd0‐catalyzed in situ coupling/cyclization/Michael addition reaction to install simultaneously two functional groups at the C4 and the C3 positions of indoles. This is followed by a Pd0‐catalyzed intramolecular cyclization which builds a seven‐membered C4, C3‐bridge. Sodium formate is used to trigger the necessary switching between the palladium catalysed reactions.

A cascade procedure for the efficient and atom‐economical synthesis of spiro[5.n (n = 6‐8)]heterocycles has been developed. This process goes through the tandem reactions of base‐promoted ring‐expansion of cyclic ketones followed by Cu‐catalyzed intramolecular C‐2 spirocyclization of indoles. Easily accessible starting materials and broad substrate scope are the advantaged features of this protocol.

An organocatalyst‐controlled site‐selectivity switchable enantioselective Friedel‐Crafts reaction of unprotected 1‐naphthols has been established for the first time via the conjugate addition of 1‐azadienes. By two chiral complementary squaramide and phosphoric acid, both ortho‐ and para‐selective Friedel‐Crafts alkylations of 1‐naphthols were independently achieved with high efficiency and enantioselectivity. With this strategy, a wide range of optically active triarylmethanes have been achieved in high yields with good to excellent enantioselectivities.

The on water reaction of sodium telluride with electrophiles has been explored. Na₂Te, generated in situ through the rongalite (sodium hydroxymethanesulfinate)‐promoted reduction of elemental tellurium, reacts with a wide variety of electrophiles, including strained heterocycles, haloalkanes, Michael acceptors, and aryl diazonium salts, providing simple and rapid access to a broad range of novel functionalised symmetrical tellurides. The methodology well tolerated the presence of versatile functional groups such as alchohols, amines, esters, nitriles, and sulfones and allowed the incorporation of tellurium atoms into biologically relevant natural‐derived products. Furthermore, in the case of the nucleophilic ring opening of epoxides, a judicious tuning of the reaction conditions enabled the synthesis of unreported β‐hydroxy‐ and β‐amino‐ditellurides, which were further employed as precursors of new functionalised unsymmetrical dialkyl tellurides. The thiol‐peroxidase catalytic activity of hydroxy‐ditellurides has also been investigated in order to compare their antioxidant properties with those of homologous tellurides.

In this work, we describe the use of Boron Dipyrromethene (BODIPY) as electron‐withdrawing group for activation of double bonds in asymmetric copper‐catalyzed [3+2] cycloaddition reactions with azomethine ylides. The reactions take place under smooth conditions and with high enantiomeric excess for a large number of different substituents, pointing out the high activation of the alkene by using a boron dipyrromethene as electron‐withdrawing group. Experimental, theoretical studies and comparison with other common electron‐withdrawing groups in asymmetric copper‐catalyzed [3+2] cycloadditions show the reasons of the different reactivity of the boron dipyrromethene derivatives, which can be exploited as a useful activating group in asymmetric catalysis. Additional experiments show that the so obtained pyrrolidines can be employed as biocompatible biosensors, which can be located in the endosomal compartments and do not present toxicity in three cell lines.

In this paper we describe an approach for the synthesis of a set of new diversely di‐substituted cyclopentenones using Morita‐Baylis‐Hillman (MBH) adducts as building blocks. The synthesis was performed with few steps, but the overall yield reached 34%. A key step of this approach is a rhodium mediated 1,4‐addition reaction on adequately functionalised MBH adducts, which leads to the creation of cinnamate ester derivatives with high E selectivity. These intermediates were used as substrates for an intramolecular Friedel‐Crafts cyclisation reaction to achieve the required 2,3‐substituted cyclopentenones. As far as we know, this is the first report to describe the synthesis of substituted cyclopentenones that directly employ MBH adducts as building blocks.

ABSTRACT. In its minimal expression, a supramolecular catalyst that acts on a single bound substrate consists of (i) a binding unit that is complementary to a non‐reacting part of the substrate, (ii) a reactive unit capable of catalyzing the reaction of the bound substrate, and (iii) a spacer connecting the two units in a geometry suitable for productive binding. When binding of two or more species is wanted, the number of binding units increases accordingly. This minireview deals with supramolecular catalysts that use crown ether units for the recognition of one or two reactants involved in a variety of reactions, including cleavage of esters and amides, hydride transfer from dihydropyridine to pyridinium, pyruvate decarboxylation, enolate allylation, radical addition to sodium metacrylate, reduction of NO 2 ˉ anion to NO, C‑H oxidation of aliphatic chains, and Diels‐Alder reactions.

Fluoroform is an interesting motif for the isotopologue labelling of biologically active compounds with fluorine‐18 for PET imaging. However, so far the building block [18F]fluoroform and consequently the [18F]trifluoromethylated products suffered from low molar activities ranging from 0.1 to 30 GBq/µmol due to isotopic dilution under the strongly basic standard radiofluorination conditions. In this article the synthesis of high molar activity [18F]fluoroform is described. By implementing a recently reported novel radiofluorination reagent, [18F]triflyl fluoride, the concentration of base‐cryptand complex in the reaction could be reduced 100‐fold compared to standard radiofluorination conditions and molar activities close to 100 GBq/µmol (at end of [18F]fluoroform synthesis) could be obtained, enabling the imaging of low density receptors. Furthermore, an automated procedure was developed on the commercially available NEPTIS® perform synthesizer to provide access of high molar activity [18F]fluoroform to other PET centres.

Synthesis, temperature dependent NMR structure investigation and utilization of a new, stable and easily accessible aryl‐diadamantylphosphine ligand family is reported. The bulky and electron rich phosphorous center of the ligand enhances the catalytic activity of palladium in cross‐coupling reactions of sterically demanded ortho substituted aryl halides. In our study we demonstrated the synthetic applicability of the new phosphine ligands in Buchwald‐Hartwig and tosyl hydrazone coupling reactions.

A one‐pot biocascade of two enzymatic steps catalyzed by a L‐lactate oxidase and a tyrosine phenol‐lyase has been successfully developed in the present study. The reaction provides an efficient method for the synthesis of L‐tyrosine derivatives, which exhibits readily available starting materials and excellent yields. In the first step, an in situ generation of pyruvate from readily available bio‐based L‐lactate catalyzed by a highly active L‐lactate oxidase from Aerococcus viridans (AvLOX) was developed (using oxygen as oxidant and catalase as hydrogen peroxide removing reagent). Pyruvate thus produced underwent C−C coupling with phenol derivatives as acceptor substrate using specially designed thermophilic tyrosine phenol‐lyase mutants from Symbiobacterium toebii (TTPL). Overall, this cascade avoids the high cost and easy decomposition of pyruvate and offered an efficient and environmentally friendly procedure for L‐tyrosine derivatives synthesis.

The present work focuses on a theoretical investigation of plausible mechanism, determination of catalytically active species, and understanding of the regioselectivity in the InCl3-catalyzed cycloaddition of N-tosyl formaldimine with alkenes or allenes. InCl3 and InCl2+ coordinated by dichloroethane (InCl2+-DCE) were investigated as model catalytic systems. DFT data supported that InCl2+-DCE represent the plausible in situ generated catalytic species. The catalytic cycle starts from the coordination of N-tosyl formaldimine to InCl2+-DCE, generating an In-complexed iminium intermediate. This then undergoes intermolecular reaction (aza-Prins) with alkene substrate to form a carbocation intermediate, which is chemoselectively attacked by the second N-tosyl formaldimine molecule to form a formaldiminium intermediate. In a final step, this intermediate undergoes the ring closure, leading to hexahydropyrimidine along with the regeneration of catalyst. In addition, our DFT results indicate that N-tosyl formaldimine not only acts as a reactant, but also accelerates the 1,3-H-shift as a proton acceptor giving an experimentally observed allylamide product. Also, the “iminium/alkene/imine” path was supported by calculation results for diastereoselective [2+2+2] reaction using an internal alkene. Finally, the regioselectivity of the InCl3-catalyzed cycloaddition using allenes along with N-tosyl formaldimine was also analyzed.