Although asymmetric thermal (2+ 2) cycloadditions have been extensively described,' photocycloadditions using two olefin components have been only reported in a few cases and lack general synthetic utility2 as well as suffering from generally low yields. A number of (2+ 2) photocycloadditions, with high stereoselectivity, have been performed in an intramolecular fa~ hion,~ while others have elaborated chiral olefins in an intermolecular ...
