Transition Metal Catalyzed [5 + 2] Cycloadditions of Vinylcyclopropanes and Alkynes: A Homolog of the Diels-Alder Reaction for the Synthesis of Seven-Membered Rings

摘要

The transition metal catalyzed cycloaddition of vinylcyclopropanes to alkynes is shown to provide a flexible and efficient route to seven-membered rings. Except for the volatile product 9e, all cycloadditions studied thus far proceed in yields of 70-95% and appear to be relatively little influenced by steric and electronic effects. A secondary reaction involving positional isomerization of the product double bond is a limitation encountered in two cases. This method establishes the experimental framework for conceptually new approaches to natural and non-natural seven-membered-ring-containing compounds and suggests a greater role for vinylcyclopropanes as diene homologues in a wide range of transition metal catalyzed reactions and more generally for the catalyzed addition of strained rings across π-systems, ideas currently under investigation.