reductive dealkylation reaction is explored and the limitations with respect to steric and electronic factors are determined. A mechanistic analysis of the reaction is described that consisted of deuterium labelling experiments and hydrogenolysis of enantioenriched derivatives. The investigation shows that the C(sp3)–C(sp3) σ bond‐cleaving events occur through a hybrid SN1/SN2 mechanism, in which the palladium
通过钯催化的C(sp 3)–C(sp 3)氢解对苄基的季碳,叔碳和仲碳中心进行修饰)呈现σ键。当在温和的氢解条件下(含钯碳和氢气的大气压)处理带有季苄基中心的苄基麦德鲁姆的酸衍生物时,就可以很好地获得高收率的芳族化合物,这些芳族化合物被叔苄基中心和麦德鲁姆酸所取代。类似地,含有叔或仲苄基中心的底物分别产生被仲苄基中心或甲苯衍生物取代的芳族化合物。此外,该策略用于二芳基甲烷的高产率合成。探索了还原性脱烷基反应的范围,并确定了对空间和电子因素的限制。描述了该反应的机理分析,该分析由氘标记实验和对映体富集的衍生物的氢解组成。调查显示,C(sp 3)–C(sp 3)σ键断裂事件是通过混合的S N 1 / S N 2机理发生的,其中钯中心置换了一个基于碳的离去基团,即Meldrum酸,其构型反转,随后通过还原消除钯来提供CH键。
Asymmetric Synthesis of All-Carbon Benzylic Quaternary Stereocenters via Cu-Catalyzed Conjugate Addition of Dialkylzinc Reagents to 5-(1-Arylalkylidene) Meldrum's Acids
作者:Eric Fillion、Ashraf Wilsily
DOI:10.1021/ja056692e
日期:2006.3.1
The asymmetric synthesis of all-carbon benzylic quaternary stereocenters has been successfully achieved through copper-catalyzed addition of dialkylzinc reagents to 5-(1-arylalkylidene) and 5-(dihydroindenylidene) Meldrum's acids in the presence of phosphoramidite ligand. The resulting benzyl-substituted Meldrum's acids and 1,1-disubstituted indanes were obtained in good yields and up to 99% ee. The significance of substituting the position para, meta, and ortho to the electrophilic benzylic center was highlighted. A benzyl Meldrum's acid product was further transformed to a 3,3-disubstituted 1-indanone and a beta,beta-disubstituted pentanoic acid.
10.15227/orgsyn092.0182
作者:Beaton, Eric、Fillion, Eric
DOI:10.15227/orgsyn092.0182
日期:——
Asymmetric Synthesis of All-Carbon Benzylic Quaternary Stereocenters via Conjugate Addition to Alkylidene and Indenylidene Meldrum’s Acids
作者:Ashraf Wilsily、Eric Fillion
DOI:10.1021/jo901559d
日期:2009.11.20
aryl group consistently leading to high enantioselectivities. The nature of the organozinc reagent on the efficiency and selectivity of the conjugateaddition was also investigated. The solid-state conformation was determined for a number of alkylidene Meldrum’s acids and correlated with the observed enantioselectivity in relation to the arene pattern of substitution.
Hydrogenolysis of Unstrained Carbon−Carbon σ Bonds: Stereoselective Entry into Benzylic Tertiary Centers
作者:Ashraf Wilsily、Yen Nguyen、Eric Fillion
DOI:10.1021/ja9076815
日期:2009.11.4
through Pd-catalyzed reductive cleavage of unstrained carbon-carbon sigmabonds is described. From the hydrogenolysis of benzyl Meldrum's acids bearing an all-carbon benzylic quaternary center, Meldrum's acid and aromatics substituted with a tertiary benzylic stereocenter were obtained in good to excellent yields. Mechanistic studies showed that the reductive cleavage of enantioenriched benzylic quaternary