Protonation of Homoenolate Equivalents Generated by N-Heterocyclic Carbenes
作者:Karl Scheidt、Brooks Maki、Audrey Chan
DOI:10.1055/s-2008-1072516
日期:2008.4
Homoenolate equivalents are generated by Lewis basic N-heterocyclic carbene catalysts and then protonated to generate efficiently saturated esters from unsaturated aldehydes. This reactivity is extended to the generation of beta-acylvinyl anions from alkynyl aldehydes. The asymmetric protonation of a homoenolate equivalent generated from a beta,beta-disubstituted aldehyde can be accomplished with a
ABSTRACT A protocol that carboxylicacids esterifies with the quaternary ammonium salt of deep eutectic solvent (DES) is presented, which opens a new access to ester using DES as alkylating agent, solvent, and catalyst. The reaction runs smoothly in DES without any other additives. Substituted cinnamic acids, aromaticacids, and aliphatic acids can be esterified in moderate to good yields. The advantages
摘要提出了一种羧酸与深共熔溶剂 (DES) 的季铵盐进行酯化的协议,它开辟了使用 DES 作为烷化剂、溶剂和催化剂获得酯的新途径。反应在 DES 中顺利进行,无需任何其他添加剂。取代的肉桂酸、芳香酸和脂肪酸可以以中等至良好的收率进行酯化。该反应的优点是官能团相容性好,反应过程简单。图形概要
Chemoselective hydrogenation using molecular sieves-supported Pd catalysts: Pd/MS3A and Pd/MS5A
Palladium catalysts embedded on molecular sieves (MS3A and MS5A) were prepared by the adsorption of Pd(OAc)(2) onto molecular sieves with its in situ reduction to Pd-0 by MeOH as a reducing agent and solvent. 0.5% Pd/MS3A and 0.5% Pd/MS5A catalyzed the hydrogenation of alkynes, alkenes, and azides with a variety of coexisting reducible functionalities, such as nitro group, intact. It is noteworthy that terminal alkenes of styrene derivatives possessing electron-donating functionalities on the benzene nucleus were never hydrogenated under 0.5% Pd/MS5A-catalyzed conditions, while internal alkenes of 1-propenylbenzene derivatives were readily reduced to the corresponding alkanes. (C) 2012 Elsevier Ltd. All rights reserved.
Synthesis of Fused Bicyclic Aminals through Sequential Gold/Lewis Acid Catalysis
A novel sequential catalysis by combining gold catalysis with early transition metal catalysis was developed. Biologically important bicyclo[4.n.0] aminals were obtained under very mild conditions.