Homochiral fluoro-organic compounds. Part 12. α-Hydroxy β-fluoro aldehydes and esters, fluoro epoxides and glycols from fluorinated sulphinyl chirons

Abstract

α-Fluoro α′-sulphinyl ketones carrying an α′-alkyl or α′-aryl substituent have been reduced with high 1,2- or 1,3-induced diastereoselectivity to give the corresponding α-fluoro α′-sulphinyl secondary alcohols. The chiral sulphinyl auxiliary agent was removed first by selective reduction to a thin group, then by methylation to a sulphonium ion and finally through S_N2 removal by the adjacent secondary alcohol. It is therefore possible to obtain, in an optically pure form, α-fluoro epoxides which are chiral at both the carbon atoms of the oxirane ring, or at the α-fluorinated carbon and at the adjacent oxirane carbon. Furthermore, homochiral α-fluorinated vicinal glycols, β-fluoro α-hydroxy aldehydes, and β-fluoro α-hydroxy esters, which may contain the fluorohydrin moiety with syn or anti relative stereochemistry, have been obtained in an optically pure form from the corresponding α-fluoro α′-sulphinyl secondary alcohols by use of the varied reactivity of the sulphinyl group.