Acyl radical cyclizations in synthesis. Part 5. Further tandem processes: formation of an α-methylenecyclohexanone by a cyclization–fragmentation hydrogen-abstraction sequence

Abstract

Two Se-phenyl 7-cyclopropyl(selenohept-6-enoate) esters were prepared and their reactions with tributylstannane and a free-radical initiator were studied. In both cases the initial acyl radical cyclization proceeded smoothly to give cyclopropylmethyl radicals which then suffered clean ring opening to homoallylic radicals. In the case of the initial substrate carrying a phenyl group at the 7-position a further radical rearrangement involving δ-hydrogen abstraction occurred to give, after chain transfer with the stannane, an α-alkylidenecyclohexanone.