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Isolation and Characterization of Regioisomers of Pyrazole-Based Palladacycles and Their Use in α-Alkylation of Ketones Using Alcohols
Organometallics ( IF 2.5 ) Pub Date : 2017-08-24 00:00:00 , DOI: 10.1021/acs.organomet.7b00478
Ramesh Mamidala 1 , Shaikh Samser 1 , Nishant Sharma 1 , Upakarasamy Lourderaj 1 , Krishnan Venkatasubbaiah 1
Affiliation  

Regioisomers of 3,5-diphenyl-1-(4-(trifluoromethyl)phenyl)-1H-pyrazole-based palladacycles (1 and 2) were synthesized by the aromatic C–H bond activation of N/3-aryl ring. The application of these regioisomers as catalysts to enable the formation of α-alkylated ketones or quinolines with alcohols using a hydrogen borrowing process is evaluated. Experimental results reveal that palladacycle 2 is superior over palladacycle 1 to catalyze the reaction under similar reaction conditions. The reaction mechanisms for the palladacycles 1 and 2 catalyzed α-alkylation of acetophenone were studied using density functional theoretical (DFT) methods. The DFT studies indicate that palladacycle 2 has an energy barrier lower than that of palladacycle 1 for the alkylation reaction, consistent with the better catalytic activity of palladacycle 2 seen in the experiments. The palladacycle–phosphine system was found to tolerate a wide range of functional groups and serves as an efficient protocol for the synthesis of α-alkylated products under solvent-free conditions. In addition, the synthetic protocol was successfully applied to prepare donepezil, a drug for Alzheimer’s disease, from simple starting materials.

中文翻译:

基于吡唑的Paladacycles区域异构体的分离,表征及其在酮类α-烷基醇合成中的应用

3,5-二苯基-1-(4-(三氟甲基)苯基)-1 H-吡唑基四氢呋喃环化合物(12)的区域异构体是通过N / 3-芳基环的芳族C–H键活化合成的。评估了这些区域异构体作为催化剂的应用,以使用氢借入过程与醇形成α-烷基化的酮或喹啉。实验结果表明,在相似的反应条件下,Palladacycle 2在催化反应方面优于Palladacycle 1。Palladacycles 12的反应机理使用密度泛函理论(DFT)方法研究了苯乙酮催化的α-烷基化反应。DFT研究表明,对于烷基化反应,Palladacycle 2具有比Palladacycle 1更低的能垒,这与在实验中看到的Palladacycle 2更好的催化活性是一致的。发现palladacycle-phosphine系统具有宽泛的官能团,可作为无溶剂条件下合成α-烷基化产物的有效方法。此外,合成方案已成功应用于从简单的起始原料制备多奈哌齐(一种用于治疗阿尔茨海默氏病的药物)。
更新日期:2017-08-24
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