Iron-Catalyzed Enantioselective Multicomponent Cross-Couplings of alpha-Boryl Radicals

Despite recent interest in the development of iron-catalyzed transformations, methods that use iron-based catalysts capable of controlling enantioselectivity in carbon-carbon cross-couplings are underdeveloped. Herein, we report a practical and simple protocol that uses commercially available and expensive iron salts in combination with chiral bisphosphine ligands to enable thåe regio- and enantioselective (up to 91:9) multicomponent cross-coupling of vinyl boronates, (fluoro)alkyl halides, and Grignard reagents. Preliminary mechanistic studies are consistent with rapid formation of α-boryl radical followed by reversible radical addition to mono-aryl bisphosphine-Fe(II) and subsequent enantioselective inner-sphere reductive elimination. From a broader perspective, this work provides a blueprint to develop asymmetric Fe-catalyzed multicomponent cross-couplings via the use of alkenes as lynchpins to translocate alkyl radicals, modify their steric and electronic properties, and induce stereocontrol.