S(H)2' reaction in organocobaloximes: Synthesis and 1,3-rearrangement of exo-methylene alicyclic allyl sulfones

Article abstract of DOI:10.1016/S0040-4020(01)80856-5

Photostimulated reactions of cyclopentenylmethyl-, cyclohexenylmethyl- and α-pinenyl cobaloximes with arenesulfonyl halides result in the formation of corresponding exo-methylene cycloalkylsulfones in 82-98% isolated yields. The product formation is rationalized by a radical chain mechanism involving an S(H)2' displacement of cobaloxime(II) from organocobaloximes by sulfonyl radical. Reaction under thermal condition, however, provides a mixture of exo-methylene cycloalkylsulfone and its endo-isomer. Independent experiments confirmed that the endo-isomer arises from a facile 1,3-allylic rearrangement of the exo-isomer. From mechanistic and theoretical studies the rearrangement is proposed to involve a [1,3]-sigmatropic migration of sulfonyl group.