Regioselective C–H bond activation of asymmetric bis(ylide)s promoted by Pd

Abstract

Asymmetric ylide–phosphonium [PhPCHC(O)CHPR]Br (PR = PPhMe 4, PPhMe 5) and bis(phosphonium) salts [PhPCHC(O)CHPR]X (PR = PPhMe 6, PPhMe 7) react with PdCl(NCMe)/NEt or Pd(OAc), respectively, to give the C,C-chelating bis(ylide) complexes [PdCl{η-[PhPCHC(O)CHPR-κ-C,C]}] (PR = PPhMe 8, PPhMe 9) regioselectively in the erythro form. Starting from 8 and 9, the corresponding halide-bridge dimers [Pd(µ-Cl){η-[PhPCHC(O)CHPR-κ-C,C]}](ClO) (PR = PPhMe 12, PPhMe 13) can be easily prepared. Complexes 12 and 13 react with bulky phosphines or diphosphines, undergoing intramolecular C–H bond activation and ortho-palladation of the C,C-chelating bis(ylide), thereby transforming the Pd{η-[PhPCHC(O)CHPR-κ-C,C]} fragment into the Pd(CH-2-PPhCHC(O)CHPR-κ-C,C) moiety in complexes 14–21. This ortho-palladation takes place with complete regioselectivity, because only the PPh unit undergoes the C–H bond activation process.