Harnessing the Silicon Effect for Copper-Catalyzed Linear-E-Selective Reductive Coupling of Ketones with Allenylsilanes.

We report a copper-catalyzed reductive coupling of ketones with allenylsilanes that delivers γ-silyl homoallylic alcohols with exceptional linear E-selectivities. Mechanistic investigations indicate that the silyl substituent functions as a directing element for regioselectivity control. DFT calculations further reveal that the allyl addition is the regio-determining step, where the branched allylcopper species shows a markedly lower activation barrier. The vinylsilane products serve as versatile platforms for downstream functionalization, enabling efficient carbon-chain elongation.