Rhodium-complex-catalyzed [2+2+2] cycloaddition of diynes and carbonyl compounds

A Rh-BINAP complex was used to catalyze the hetero-[2+2+2] cycloaddition of symmetrical 1,6-diynes and carbonyl moiety of ketoesters, a diketone, and an aldehyde to give bicyclic α-pyrans, which were readily transformed into monocyclic compounds via the following electrocyclic ring opening. In the reaction of an unsymmetrical 1,6-diyne and a 1,7-diyne, α-pyrans with a quaternary carbon stereocenter were obtained in moderate to excellent ee using a chiral rhodium catalyst.