Photoredox Iridium Catalyst for Single Electron Transfer (SET) Cross-Coupling

Introduction

C(sp²)- and C(sp)-hybridized coupling reactions are established catalytic approaches. However, multi-step C(sp³)- and C(sp²)-coupling reactions of boronic acids and related derivatives are still limited by ineffective two-electron transmetalation reactions. These conventional protocols exhibit reactivity profiles related to heterocyclic C-B bond strengths, thereby greatly impeding progress toward efficient cross-coupling of C(sp³)-hybridized alkylboron nucleophiles.

Recently, a series of efficient, single-election transmetalation methods have been optimized for alkyl cross-coupling using a dual-catalyst system of nickel (244988) and iridium (804215) catalysts, whereby a potassium organotrifluoroborate is activated for cross-coupling via oxidative fragmentation to an alkyl radical. This mechanistic paradigm allows reactivity to be dictated by homolytic bond strengths, opening a new realm of possibilities in alkylboron cross-coupling. In collaboration with the Gary Molander group, we now offer a novel catalyst for high-yielding SET reactions.

Advantages

• Previously unrealistic C(sp³)-coupling reactions are now an efficient reality
• Reaction is performed at room temperature
• Possibilities for asymmetric coupling
• Reductive elimination using a chiral nickel catalyst allows stereoconvergent synthesis from racemic organotrifluoroborate substrates

Special thanks to Mr. John Tellis and Prof. Gary Molander for contributing this technology spotlight.