Abstract

Continuous Flow Metallaphotoredox Stereodivergent Semi-hydrogenation and Semi-deuterogenation of Alkynes

Wai Chung Fu, Assistant Professor, City University of Hong Kong

Alkenes are ubiquitous structural motifs in pharmaceuticals, agrochemicals, and materials science, while their stereoselective synthesis has been a pivotal endeavour in organic chemistry.  Stereoselective semi-hydrogenations provide straightforward access to both E- and Z-alkenes from readily available alkyne precursors, but traditional methods often suffer from poor scalability, over-reduction, limited substrate scope, and reliance on hydrogen gas.  Herein, we discuss two metallaphotoredox systems that enable stereodivergent semi-hydrogenation and semi-deuterogenation of alkynes.  We reveal new factors that control the stereoselectivity of both reactions, such as by varying the acid co-catalysts or the residence time in flow.  Both E- and Z-alkenes are obtained with excellent stereoselectivity and broad functional group tolerance.  Water serves as the primary hydrogen source, while cost-efficient and readily available reagents and ligands are used.  Our reactions can be readily scaled-up in flow without compromising yield and stereoselectivity.