Mechanism of Z-Selective Hydroalkylation of Terminal Alkynes

Abstract

This paper describes a detailed mechanistic study of the silver-catalyzed Z-selective hydroalkylation of terminal alkynes. Considering the established mechanistic paradigms for Z-selective hydroalkylation of alkynes, we explored a mechanism based on the radical carbometalation of alkynes. Experimental results have provided strong evidence against the initially proposed radical mechanism and have led us to propose a new mechanism for the Z-selective hydroalkylation of alkynes based on boronate formation and a 1,2-metalate shift. The new mechanism provides a rationale for the excellent Z-selectivity observed in the reaction. A series of stoichiometric experiments has probed the feasibility of the proposed elementary steps and revealed an additional role of the silver catalyst in the protodeboration of an intermediate. Finally, a series of kinetic measurements, KIE experiments, and competition experiments allowed us to identify the turnover limiting step and the resting state of the catalyst. We believe that the results of this study will be useful in the further exploration and development of related transformations of alkynes.

Z∶E Selective Preparation of Disubstituted Internal Alkenes and Trisubstituted Alkenes

“…机理研究表明, 硼酸 银中间体的 1,2-金属酸盐重排是决定反应立体化学结果 的关键步骤. 2021 年, 该课题组 [48] 详细研究了银催化末 端炔的 Z-选择性氢烷基化反应机理, 探索了一种基于炔 基碳金属化反应的机理, 反应机理如 Scheme 14 所示.…”

“…图式 14 银催化的炔烃的氢烷基化反应可能的反应机理 Scheme 14 Possible mechanism of hydrogenalkylation of alkynes catalyzed by silver Reproduced from Ref. [48] with permission from the American Chemical Society 图式 15 苯乙酸直接脱羧消除制备烯烃 Scheme 15 Preparation of olefin by direct decarboxylation of phenylacetic acid Reproduced from Ref. [49] with permission from the American Chemical Society 组 [50] 描述了一种铜催化的环氧化合物区域选择性和立 体定向脱氧制备烯烃的反应.…”

Ligand-Controlled Cobalt-Catalyzed Regiodivergent Alkyne Hydroalkylation

“…Recently, base-metal-catalyzed alkyne hydrofunctionalization has emerged as an alternative method to access functionalized alkenes, encompassing the formal addition of a hydrogen and a functional group to the alkynyl triple bonds. − Alkyne hydroalkylation is always highly versatile and stereocontrolled to produce various isomers of alkenes, including 1,1-disubstituted alkenes, 1,2-disubstituted alkenes, and trisubstituted alkenes . For example, copper hydride ,,, and nickel hydride ,, are regio- and stereoselectively inserted into alkynes to generate corresponding organometallic species via ( E )- anti -Markovnikov and Markovnikov additions, respectively .…”

Origins of regio- and stereoselectivity in Cu-catalyzed alkyne difunctionalization with CO2 and organoboranes

“…In addition, the acidic C(sp)–H of terminal alkynes can be expected to form alkynyl metal species, 4 which could readily react with electrophilic trialkyl boranes to generate alkynyl boronate complexes ( III , Scheme 2b). Based on the previously recognized 1,2-migration of alkyl, alkenyl/aryl and alkynyl boronate complexes, 5 the boron-substituted alkenyl copper( iv ) intermediate could be formed via 1,2-migration. Subsequent M–C bond protonation, transmetalation and CO 2 insertion lead to the geminal addition products.…”