Breaking News on the Enantioselective Intermolecular Heck Reaction

摘要

The Heck reaction is one of the fundamental palladium(O)-catalyzed C—C bond-forming reactions, and its impact on the way molecules are built today was recognized with the Nobel Prize in Chemistry. The breadth and depth of research dedicated to its various facets over the past decades'1' leaves the erroneous impression that Heck chemistry is now a mature area. The mechanistic understanding of how the countless parameters of a Heek reaction affect its outcome is still premature, and that includes the subtle factors that govern the regioselectivity of the migratory insertion as well as the β-hydride elimination. These issues are particularly evident in intermolecular scenarios with internal (sterically and electronically nonbiased) alkenes. The inability to control these steps in a predictable manner is likely to account for the limited progress in the asymmetric variant. Enantioselective intermolecular Heck reactions usually require cyclic alkenes where conformational rigidity and, hence, restricted rotation around C—C bonds steers β-hydride elimination away from the newly formed C—C bond (Figure 1, left).