Palladium-catalyzed reactions of hypophosphorous compounds with allenes, dienes, and allylic electrophiles: Methodology for the synthesis of allylic H-phosphinates

Article abstract of DOI:10.1021/jo702542a

(Chemical Equation Presented) Hypophosphorous compounds (MOP(O)H ₂, M = H, R₃NH) effectively participate in metal-catalyzed C-P bond-forming reactions with allenes, dienes, and activated allylic electrophiles under mild conditions. The catalytic system Pd₂dba ₃/xantphos is crucial to avoid or minimize the competitive reductive transfer-hydrogenation pathway available to hypophosphorous acid derivatives. Further investigation into the allylation mechanism provided access to the analogy allylic acetate - allylic phosphinate, which then led to the development of a Pd-catalyzed rearrangement of preformed allylic phosphinates esters and, ultimately, to a catalytic dehydrative allylation of hypophosphorous acid with allylic alcohols. The reactions disclosed herein constitute efficient synthetic approaches, not only to prepare allylic H-phosphinic acids but also their esters via one-pot tandem processes. In addition, the potential of H-phosphinates as useful synthons for the preparation of other organophosphorous compounds is demonstrated.