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.