Reported herein is a visible‐light‐mediated radical approach to the α‐alkylation of ketones. This method exploits the ability of a nucleophilic organocatalyst to generate radicals upon SN2‐based activation of alkyl halides and blue light irradiation. The resulting open‐shell intermediates are then intercepted by weakly nucleophilic silyl enol ethers, which would be unable to directly attack the alkyl
Nucleophilic reactions of various enol silylethers with carbocation species generated from propargylsilylethers by the action of a Lewis acid have been developed. The present method is highly useful for the introduction of allenic or enyne functionalities into the alpha-position of substituted ketones. [reaction--see text]
Synthesis of γ-substituted carbonyl compounds from DMSO-mediated oxidation of enynamides: mechanistic insights and carbon- and hetero-functionalizations
作者:Quynh H. Nguyen、Nguyen H. Nguyen、Hanbyul Kim、Seunghoon Shin
DOI:10.1039/c9sc03663f
日期:——
aliphatic alcohols, thiols, and hydrazides, could be efficiently alkylated at the γ-position in a highly regioselective fashion. The kinetic analysis suggested a nucleophile-dependent mechanism ranging from a concerted SN2′′ to a carbocationic mechanism. Thus, the remote site-selectivity was ascribed to the partial positive charge developing at the terminal carbocationic center.
已经开发了使用 DMSO 作为末端氧化剂的 1,3-烯酰胺的氧化偶联。碳以及未修饰的杂原子亲核试剂,包括脂肪醇、硫醇和酰肼,可以在 γ 位以高度区域选择性的方式有效地烷基化。动力学分析表明了一种亲核试剂依赖性机制,范围从协同的 S N 2'' 到碳阳离子机制。因此,远程位点选择性归因于在末端碳阳离子中心产生的部分正电荷。
Novel Carbon−Carbon Bond-Forming Reactions Using Carbocations Produced from Substituted Propargyl Silyl Ethers by the Action of TMSOTf
stable allenyl, propargyl, or allyl-propargyl hybrid cations have been developed. These carbocations could be generated from silyl 1-(pi-donor)-substituted propargylethers by the action of trimethylsilyl trifluoromethanesulfonate in dichloromethane at -78 degrees C to room temperature and could be attacked nucleophilically by electron rich arenes, allylsilanes, or enol silyl ethers, giving rise to
Silyl dienol ethers prepared from α,β-unsaturated ketones underwent nickel-catalyzed difluorocyclopropanation of the electron-rich alkene moiety with trimethylsilyl 2,2-difluoro-2-(fluorosulfonyl)acetate. The subsequent vinylcyclopropane–cyclopentene rearrangement afforded silyl 5,5-difluorocyclopent-1-en-1-yl ethers in good yields. The obtained five-membered silyl enolethers were demonstrated to