Bifunctional Ligand-Assisted Catalytic Ketone α‑Alkenylation with Internal Alkynes: Controlled Synthesis of Enones and Mechanistic Studies

Here,
we describe a detailed study of the rhodium­(I)-catalyzed,
bifunctional ligand-assisted ketone α-C–H alkenylation
using internal alkynes. Through controlling the reaction conditions,
conjugated enamines, α,β- or β,γ-unsaturated
ketones, can be selectively accessed. Both aromatic and aliphatic
alkynes can be employed as coupling partners. The reaction conditions
also tolerate a broad range of functional groups, including carboxylic
esters, malonates, secondary amides, thioethers, and free alcohols.
In addition, excellent E-selectivity was observed
for the tetra-substituted alkene when forming the α,β-unsaturated
ketone products. The mechanism of this transformation was explored
through control experiments, kinetic monitoring, synthesizing the
rhodium–hydride intermediates and their reactions with alkynes,
deuterium-labeling experiments, and identification of the resting
states of the catalyst.

我们在此报道一项关于铑(I)催化、双功能配体辅助下以内炔烃为偶联底物的酮α-C-H烯基化反应的详细研究。通过调控反应条件，可选择性得到共轭烯胺、α,β-或β,γ-不饱和酮。芳香族与脂肪族炔烃均可作为偶联配偶体使用。该反应条件可兼容多种官能团，包括羧酸酯、丙二酸酯、二级酰胺、硫醚以及游离醇。此外，在生成α,β-不饱和酮产物时，四取代烯烃可获得优异的E型选择性。本研究通过控制实验、动力学监测、铑氢中间体的合成及其与炔烃的反应、氘标记实验以及催化剂休眠态的鉴定，对该转化的反应机理进行了探究。