Rhodium-Catalyzed Regio-, Diastereo-, and Enantioselective [2+2+2] Cycloaddition of 1,6-Enynes with Acrylamides

摘要

Transition-metal-catalyzed intermolecular [2+2+2] cycload-ditions of α,ω-diynes or enynes with unsaturated compounds are valuable methods for the synthesis of complex bicyclic molecules in a single step. For example, the transition-metal-catalyzed [2+2+2] cycloaddition of 1,6-enynes with alkynes enables the facile preparation of densely substituted annulated cyclohexadienes. In 2005, the groups of Evans and Shibata developed asymmetric variants of this reaction that furnish annulated cyclohexadienes with one stereogenic center by using cationic rhodium(I)/chiral bisphosphine complexes as catalysts (Scheme 1). Additionally, it has been reported that the cationic rhodium(I)/chiral bisphosphine complexes catalyze the asymmetric [2+2+2] cycloaddition of 1,6-diynes with electron-deficient alkenes, to also afford annulated cyclohexadienes with one stereogenic center (Scheme 1).