Site-Selective Csp3-Csp/Csp3-Csp2 Cross-Coupling Reactions Using Frustrated Lewis Pairs

The donor-acceptor ability of frustrated Lewis pairs (FLPs) has led to widespread applications in organic synthesis. Single electron transfer from a donor Lewis base to an acceptor Lewis acid can generate a frustrated radical pair (FRP) depending on the substrate and energy required (thermal or photochemical) to promote an FLP into an FRP system. Herein, we report the C cross-coupling reaction of aryl esters with terminal alkynes using the B(CP FLP. Significantly, when the 1-ethynyl-4-vinylbenzene substrate was employed, the exclusive formation of cross-coupled products was observed. However, when 1-ethynyl-2-vinylbenzene was employed, solvent-dependent site-selective C cross-coupling resulted. The nature of these reaction pathways and their selectivity has been investigated by extensive electron paramagnetic resonance (EPR) studies, kinetic studies, and density functional theory (DFT) calculations both to elucidate the mechanism of these coupling reactions and to explain the solvent-dependent site selectivity.

Automated summary

The donor-acceptor ability of frustrated Lewis pairs has been widely used in organic synthesis. Single electron transfer can generate a frustrated radical pair, leading to different reaction pathways and selectivity depending on the substrate and energy required. Investigation using EPR studies, kinetic studies, and DFT calculations has helped elucidate the mechanism of these coupling reactions and explain solvent-dependent site selectivity.