Photochemically and Thermally Induced Free-Radical Reactions of α,β-Epoxy Ketones with Tributyltin Hydride: Selective Ca-O Bond Cleavage of Oxiranylmethyl Radicals Derived from α,β-Epoxy Ketones

Article abstract of DOI:10.1021/jo00046a016

Free-radical reactions of α,β-epoxy ketones with tributyltin hydride have been studied.These substances were selectively converted to β-hydroxy ketones under both photochemical and thermal conditions.The photoreaction is initiated by hydrogen abstraction of an epoxy ketone triplet from tributyltin hydride, while azoisobutyronitrile is used as an initiator for the thermal reaction.In general, the photoreaction conditions are particularly useful for aroyl-substituted epoxy ketones while the thermal conditions are applicable to a variety of epoxy ketones.It was also found that the epoxy esters and epoxy alcohols did not undergo the ring-opening reaction under the similar conditions.Tributyltin radical attack on the carbonyl of epoxy ketones is a key process for both the photoreaction and the thermal reaction.Regioselective ring opening of the resulting oxiranylmethyl radical finally produces β-hydroxy ketones.In order to capture the free-radical intermediates, the reaction of epoxy ketones with allyltributyltin was conducted.The isolation of α-allylated β-hydroxy ketones is interpreted by the involvement of a novel 1,5-tributyltin transfer.