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。
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
Boron/zinc exchange for the conjugate arylation of unsaturated Meldrum’s acid derivatives
作者:Micaela Jardim、Lucas L. Baldassari、Maria Eduarda Contreira、Angélica V. Moro、Diogo S. Lüdtke
DOI:10.1016/j.tet.2020.130967
日期:2020.12
approach for the conjugate arylation reaction of unsaturated Meldrum’s acid derivatives is reported. The reaction takes place through a Boron-Zinc exchange reaction between arylboronic acids and diethylzinc and the subsequent transfer of thus generated reactive aryl groups to the β-position of the double bond of the Meldrum’s derivatives. The compounds obtained are valuable synthetic intermediates and
Micro-flow heteroatom alkylation <i>via</i> TfOH-mediated rapid <i>in situ</i> generation of carbocations and subsequent nucleophile addition
作者:Yuma Matsuura、Shinichiro Fuse
DOI:10.1039/d3cc06308a
日期:——
A rapid nucleophilic substitution reaction was developed using carbocations generated from diarylmethanol and trifluoromethanesulfonic acid. Undesired reactions caused by the carbocations were suppressed, presumably due to the rapid and uniform generation of carbocations and the subsequent rapid and uniform distribution of nucleophiles by the micro-flow technology.