Photochemical behaviour of ω-thiabicyclo[3.n.1]alkan-3-one: a mechanistic and exploratory study

Abstract

The photoreactivity of 9-thiabicyclo[3.3.1]nonan-3-one 9 is investigated under a variety of conditions and compared with those of its monocyclic or norbicyclic analogues 1 and 4. The principal reaction of ketone 9 on irradiation in tert-butyl alcohol is the Norrish type I cleavage to yield tert-butyl (cis-6-methyltetrahydrothiopyran-2-yl)acetate 10a, while compounds 1 and 4 give ring-contracted thilactones 2 and 5. The origin of the different chemoselectivity is discussed. Characteristic photoreactivity of ketone 9, observed upon direct irradiation in methanol, leading to the predominant formation of the endo- alcohol endo-11 can be explained by assuming the charge-transfer interaction between the sulfur and the carbonyl moiety in the photo-excited state.