Photolyses of organocobaloxime having aralkyl and (alkylthio)carbonyl groups on the β-position. A radical reaction involving the thioester group

[2-[(Alkylthio)carbonyl]-4-mesityl-2-methylbutyl]cobaloxime (1), [2-[(alkylthio)carbonyl]-2-(ethoxycarbonyl)-5-phenylpentyl]cobaloxime (2), and [2-[(alkylthio)carbonyl]-2-(ethoxycarbonyl)-4-mesitylbutyl]cobaloxime (3) were photolyzed to produce pairs of organo radicals and cobaloxime(II) radicals by the rupture of a carbon-cobalt σ-bond. The organo radicals collapsed into hydrogen abstraction products 4, 7, and 10, a thioester rearranged product, 5, an intramolecular 1,5-hydrogen shift product, 8, a thioester elimination product, 11, and β-thiolactones 6, 9, and 12. The β-thiolactones resulted by the radical substitution on sulfur of the thioester and are the major products from the cobaloximes that have a (tert-butylthio)carbonyl group. For the thioester rearrangement a stepwise mechanism is proposed, which involves an internal radical attack on sulfur followed by the bond switching from alkylthio to alkylcarbonyl (Scheme V). Last, the possible involvement of cobaloxime(II) in this thioester rearrangement is discussed. The cobalt complex is considered to facilitate the rearrangement by the interaction between sulfur and cobalt(II) radical species.