Palladium(II)-catalyzed synthesis of alpha-alkylidene-gamma-butyrolactams from N-allylic 2-alkynamides. Total synthesis of (+/-)-isocynodine and (+/-)-isocynometrine.

An efficient method for preparing alpha-alkylidene-gamma-butyrolactams via the Pd(II)-catalyzed cyclization of acyclic N-allylic 2-alkynamides via halopalladation, intramolecular olefin insertion, and beta-heteroatom elimination was developed. The reaction is less influenced by the leaving group and the concentration of the halide ions in comparison with the cyclization of acyclic alkynoates. The total syntheses of (+/-)-isocynodine and (+/-)-isocynometrine were realized using this method.