Solid‐State Photocyclodimerization of 1‐Thiocoumarin (= 2<i>H</i>‐1‐Benzothiopyran‐2‐one)

Abstract

Abstract Irradiation (λ &gt; 390 nm) of 2 H ‐1‐benzothiopyran‐2‐one ( 1 ) in the solid state affords selectively 6aα,6bα,12bα,12cα ‐tetrahydrocyclobuta[1,2‐ c :4,3‐ c ′]bis[1]benzothiopyran ‐6,7‐dione ( 2 ), the head‐to‐head ( HH ) cis ‐ cisoid‐cis ‐dimer, while irradiation of 1 in the solid state using shorter wavelengths (λ &gt; 340 nm) affords a mixture of all four cis ‐fused tricyclic dimers 2 – 5 . These results represent a novel wavelength effect in solid‐state photochemistry.