Photocycloaddition of Thiocarbonyl Compounds to Multiple Bonds. VII. The Reaction of Thiobenzophenone with Acetylenic Compounds

Photocycloaddition of thiobenzophenone to acetylenic compounds, R–C≡C–R′ (R=COOH, Ph, CH2OH, and CN; R′=H: R=COOMe; R′=COOMe), affords 1-phenyl-2-thia-1,2-dihydronaphthalene derivatives. The key step to the product is an intra-molecular aromatic substitution of the composite vinylic biradical 13. The difference in reactivity of acetylenic and olefinic compounds as well as that between thiobenzophenone and benzophenone are discussed. Ethoxyacetylene does not undergo the reaction. This is interpreted in terms of electronegativity of a radical center in 13. It is found that cyanoacetylene reacts with butanethiyl radical in contrast to its olefin analog, acrylonitrile.