Catalytic asymmetric synthesis of quaternary carbon centers by intramolecular Heck reaction: Synthetic developments and mechanistic studies

Within the last decade, the enormous synthetic potential of the Heck reacti on has been revealed. When employed intramolecularly, Heck reactions succee d in even forming quaternary carbon centers. The ability of intramolecular Heck reactions to reliably fashion carbon-carbon bonds in polyfunctional mo lecules has led to wide application of this reaction at the strategy level for the synthesis of complex natural products. One of the most important de velopments in this area is the increasing success being realized in effecti ng catalytic asymmetric Heck reactions using enantiopure ligands. Although only modest enantiocontrol was achieved in early stages, many asymmetric He ck reactions have now been demonstrated that proceed with >90% ee. Another development of the Heck reaction has led to greater understanding of its me chanistic details with two distinct pathways, the neutral and cationic path ways, being recognized. This review summarizes the synthetic developments o f the intramolecular asymmetric Heck reaction for forming quaternary carbon centers and the mechanistic factors recently revealed to effect enantiosel ectivity.