Palladium(II)-Catalyzed Synthesis of α-Alkylidene-γ-butyrolactamsfrom N-Allylic 2-Alkynamides. Total Synthesis of (±)-Isocynodineand (±)-Isocynometrine
An efficient method for preparing α-alkylidene-γ-butyrolactams via the Pd(II)-catalyzed cyclizationof acyclic N-allylic 2-alkynamides via halopalladation, intramolecular olefin insertion, andβ-heteroatom elimination was developed. The reaction is less influenced by the leaving group andthe concentration of the halide ions in comparison with the cyclization of acyclic alkynoates. Thetotal syntheses of (±)-isocynodine and (±)-isocynometrine were realized using this method.