Photo/Cerium Co-Catalyzed Hydroalkylation of Alkynes Via Decarboxylative Ring-Opening of Cyclic Carboxylic Acids.

Abstract

Hydroalkylation of alkynes serves as a pivotal strategy for the construction of polysubstituted alkenes. However, its reaction efficiency, substrate scope, and regioselectivity are highly dependent on the structures and reactivities of both the alkynylation reagent and the hydrogen-transfer reagent. This dependence leads to common bottlenecks such as poor structural tunability, low atom economy, and side reactions often caused by the hydrogen-transfer reagent. Herein, we develop a method that combines hydroalkylation of alkynes with decarboxylative ring-opening of cyclic carboxylic acids, where the cyclic carboxylic acid simultaneously serves as the alkynylation reagent and the proton donor. By tuning the substituents and ring size of the cyclic carboxylic acid, diverse substituents can be introduced into the products. In this transformation, the cyclic carboxylic acid undergoes decarboxylative ring-opening via the ligand-to-metal charge transfer (LMCT) process to generate a long-chain alkyl radical, which subsequently adds to an alkyne to give an alkenyl radical. The alkenyl radical is then reduced to an alkenyl anion by Ce(III), and final protonation delivers polysubstituted alkenes. Through cyclic voltammetry, UV-vis absorption spectroscopy, radical trapping, intermediate conversion, and H/D exchange experiments, we demonstrate the involvement of the LMCT process and that the carboxylic acid acts as the sole proton donor.