Pd-Catalyzed Umpolung of π–Allylpalladium Intermediates: Assembly of All-Carbon α‑Vinyl Quaternary Aldehydes through C(sp³)–C(sp³) Coupling

Construction of sterically congested all-carbon quaternary centers represents a formidable challenge in synthetic chemistry. The method described herein provides direct and facile access to a series of structurally diverse and synthetically useful aliphatic aldehydes, bearing an all-carbon α-vinyl quaternary center and a 1,5-diene functionality, through Pd-catalyzed umpolung of vinylethylene carbonates (VECs). The reaction features electrophilic-to-nucleophilic reactivity reversal of the VEC-derived π-allyl-palladium intermediate via an unusual β-hydride elimination process, and the resultant enolate is chemoselectively coupled with allylic acetate to form an α-vinyl aldehyde embedded with an all-carbon quaternary center.