Trans-Spanning Ligands Promote Pd-Catalyzed α-Hydroalkenylation and -Hydroalkynylation of Activated Olefins

The palladium-catalyzed “regioreversed” α-hydroalkenylation and -hydroalkynylation of conjugated alkenes is re-ported. The unconventional selectivity of this reaction is achieved through the utilization of trans-spanning bidentate phosphine ligands that stabilize the proposed trans-Pd(II)Ln(R)(H) (R = alkenyl or alkynyl) intermediate. The α-hydrofunctionalization methods tolerate a variety of electron-deficient alkenes including α,β-unsaturated amides, esters and vinyl pyridines. A range of different alkenyl/alkynyl bromides are demonstrated to be effective coupling partners in the reaction. The phosphine-ligated palladium catalyst operates under mild weakly basic or neutral conditions and is resistant to air and moisture, giving rise to practical methodology for construction of β,γ-unsaturated carbonyl compounds.