Vanadium-Catalyzed Coupling of Allenols with Electrophilic Halide Sources for the Formation of α-Halo-α′,β′-unsaturated Ketones

A vanadium-catalyzed coupling of allenylic alcohols with electrophilic halide sources to form alpha-halo-alpha',beta'-unsaturated ketones is described. The process proceeds through a metal enolate formed from the 1,3-transposition of an allenol that is initiated by a cheap and earth-abundant vanadium oxo catalyst. Fluorine, chlorine, and bromine electrophiles can be utilized, and the resulting products can give rise to the introduction of nitrogen, oxygen, sulfur, and iodine nucleophiles a to the ketone through substitution chemistry.