Regioselective formation of silylated cyclobutenes by the photochemical [2+2] cycloaddition of 2(5H)-furanones to trialkylsilylacetylenes

Enantiopure 5-alkyl-4-methyl-2(5H)-furanones reacted by [2+2] photochemical cycloaddition with several trialkylsilylacetylenes to afford regioselectively 3-oxabicyclo[3.2.0]hept- 6-en-2-ones silylated at the vinylic C-7 atom. The possible reasons for such regioselectivity are discussed. The anti/syn stereoselectivity of the photocycloaddition depends on the nature of the alkyl group on the silicon atom in the starting silylacetylenes.