CYCLIZATION REACTIONS OF ALLYLIC O-STANNYL KETYLS

This is a summary of an investigation of the tributyltin hydride-induc ed cyclization reactions of unsaturated ketones with electronically de ficient olefins. This reaction was initiated by an O-stannyl ketyl for med by the addition of a tributyltin radical to a carbonyl, which has both anionic and radical character. The intramolecular coupling produc ed functionalized cyclopentanes, bearing two synthetically useful carb on appendages. An activating or electron-withdrawing function on the a lkene was essential to the cyclization. A dilution study revealed that excellent anti stereoselectivities (>50:1) could be achieved, and thi s was attributed to a reversible cyclization. Another goal of this stu dy was to separate the radical reactivity from the anionic reactivity of the O-stannyl ketyl by the participation of labile functional group s and external electrophiles. The presence of minor products and enola te-trapping studies demonstrated that the anionic character of the ket yl could be utilized in the form of a tin enolate. This work represent s the first free radical- and reagent-based approach to the study of t he intramolecular hydrodimerization of activated alkenes.