Enantioselective Intramolecular [2 + 2 + 2] Cycloaddition of 1,4-Diene-ynes:A New Approach to the Construction of Quaternary Carbon Stereocenters

摘要

Transition-metal-catalyzed cycloaddition is an atom-economical and powerful tool for the synthesis of cyclic carbon skeletons.Various cycloadditions,including more than two alkyne and/or alkene moieties as reaction components,have been reported using transition metal catalysts.In particular,[2 + 2 + 2] cycloaddition is a general protocol for the synthesis of six-membered ring systems,and intramolecular [2 + 2 + 2] cycloaddition gives a tricyclic compound in one pot.The starting material can be classified into three types(Scheme 1):(1)the two reaction components(i.e.,alkyne(s)and/or alkene(s))are connected by a 1,2-disubstituted alkyne and triynes are most commonly used;(2)the two reaction components are connected by a 1,2-disubstituted alkene;(3)the two synthetic units are connected by a 1,1-disubstituted alkene.