4,4-Dich1oro-2-cyclobutenones 1, available by cycloaddition of acetylenes to dichloroketene, can be photolyzed in the presence of olefins or dienes to produce regiospecifically 2-vinylcyclobutanones 3-11. The photochemical reaction succeeds even in some cases where thermolysis fails and was shown to proceed by electrocyclic ring opening to a vinylketene. Stereochemically the results of photolysis of 1 differ from thermolysis with identical olefinic substrates.
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Support of this research by a grant from the Israel Academy of Sciences