Intramolecular enantioselective Mizoroki-Heck reactions of 2-alkenyl (o-halobenzyl)pyrroles

Asymmetric Mizoroki-Heck reaction is one of most important palladium(0)-catalyzed C-C bond-forming reactions, which has allowed the preparation of optically active molecules with tertiary and quaternary stereocenters. In particular, Heck-Heck cascade reactions are a powerful synthetic strategy for rapidly increasing structural and stereochemical complexity, allowing the construction of polycyclic frameworks in a one-pot operation. For this purpose, the σ-alkylpalladium intermediate, resulting from the migratory insertion of the arylpalladium to the alkene, may undergo an insertion with an alkene in inter- or intramolecular way, so carbopalladation is repeated one or several times prior to b-hydride elimination. In connection with our work in palladium-catalyzed reactions,[1] we have developed the enantioselective palladium-catalyzed Heck-Heck cascade reaction of N-benzyl 2,3-dialkenylpyrroles, using chiral ligands for palladium. A 6-exo Mizoroki–Heck reaction generates the quaternary stereocenter, giving rise to the s-alkylpalladium intermediate that undergoes a 6-endo insertion to give the Lycorane framework. Details of these transformations will be given.