Free radical-mediated reduction and deoxygenation of epoxides

Abstract

the ring opening will be guided by the relative stability of the intermediate radicals rather than the ease of approach of the hydride reagent such as in the classical SN2-type reduction condition~,~~ we would expect different product distributions under these condition^.^^*^ These expectations have been borne out, and in this communication we report our preliminary results in this area. We also report applications of related chemistry for the deoxygenation of highly functionalized epoxides including epoxy nucleosides. The resulting compounds are potential intermediates for the synthesis of dideoxy nucleosides used in anti-AIDS chem~therapy.~ Dropwise addition of 1.05 equiv of a THF solution of Cp,TiCI to a mixture of I ,I‘-epoxyethylcyclohexane and IO mmol of cyclohexa- 1 ,4-diene in THF at room temperature followed by acidic (1 N HCI) workup yielded 92.0% of I-cyclohexylethanol. Minor amounts (1.5% and 0.9% respectively) of I-ethyl-I-cyclohexanol and 1 -( 1 -chlorocyclohexyl)ethanol were also isolated. With lithium triethylborohydride, as expected, the only product formed is 1ethyl-I-cyclohexanol (eq la,b).