Electrophile-Dependent Chemo- and Regioselectivity in Cu/Pd-Catalyzed Allylboration of Enynes

Abstract

Achieving chemo- and regiodivergence from common starting materials represents a central goal in organic synthesis to enable rapid access to structurally distinct molecular architectures. Herein, we report an electrophile-controlled, chemo- and regioselective allylboration of 1,3-enynes with allylic carbonates and bis(pinacolato)diboron. The nature of the carbonate electrophile dictates the reaction outcome, with allyl carbonates enabling the efficient synthesis of borylated 1,4-enallenes, whereas dienyl carbonates redirect the transformation toward propargylation, furnishing 1,3,7-dienynes with high regio- and stereoselectivity. DFT calculations reveal that this divergence originates from distinct reductive elimination pathways of a common η3-allyl-η1-allenyl Pd intermediate, which governs selectivity. Allyl-derived intermediates undergo 1,1′-type reductive elimination to afford tetrasubstituted allenes, whereas vinyl-substituted allyl-Pd species formed from dienyl carbonates engage in an intramolecular propargylic addition. This study provides mechanistic insights into allyl–allenyl palladium chemistry and establishes a regiodivergent strategy for accessing densely functionalized organoboronates from readily available starting materials.