Cyclization Reactions of Allylic O-Stannyl Ketyls

Article abstract of DOI:10.1021/jo00120a031

This is a summary of an investigation of the tributyltin hydride-induced reactions of unsaturated ketones with electronically deficient olefins.This reaction was initiated by an O-stannyl ketyl formed by the addition of a tributyltin radical to a carbonyl, which has both anionic and radical character.The intramolecular coupling produced functionalized cyclopentanes, bearing two synthetically useful carbon appendages.An activating or electron-withdrawing function on the alkene was essential to the cyclization.A dilution study revealed that excellent anti stereoselectivities (>50:1) could be achieved, and this was attributed to a reversible cyclization.Another goal of this study was to separate the radical reactivity from the anionic reactivity of the O-stannyl ketyl by the participation of labile functional groups and external electrophiles.The presence of minor products and enolate-trapping studies demonstrated that the anionic character of the ketyl could be utilized in the form of a tin enolate.This work represents the first free radical- and reagent-based approach to the study of the intramolecular hydrodimerization of activated alkenes.