Divergent Synthesis of Chiral δ-Boryl Ketones via Copper-Catalyzed Carbonylative 1,4-Borylallylation

We herein describe a copper-catalyzed asymmetric carbonylative 1,4-borylallylation of methylenecyclopropanes (MCPs). A single copper catalyst mediates a five-component coupling of MCPs, HBpin, silane, allyl phosphates, and carbon monoxide (CO) with high chemo-, regio-, and enantioselectivity. A key feature of this methodology is its condition-dependent divergence: by subtly modulating the base and silane reagent, the reaction can be precisely steered to selectively produce one of three distinct classes of valuable chiral δ-boryl ketones: direct allylic ketones, isomerized α,β-unsaturated ketones, or fully reduced saturated ketones. All products are obtained in good yields and with high enantioselectivities. Furthermore, in the absence of CO, the catalytic system performs a direct 1,4-borylallylation, providing efficient access to chiral allylic boranes. This work presents a powerful and flexible strategy for the rapid construction of diverse and synthetically useful chiral building blocks from simple starting materials.