Phosphoranes et thio-oxazaphospholidines d'aldohexoses protégés. Synthèses et études stéréochimiques

Abstract

The alkoxyphosphoranes 1–5 have been obtained by the reaction between the bicyclophosphane 6 and the five following alcohols: 1,2,3,4-di-O-isopropylidene-α-D-galactopyranose 7, 1,2,5,6-di-O-isopropylidene-α-D-glucofuranose 8, methanol, isopropanol, and tertiobutanol. The sulfuration of 1–5 yields to the corresponding thio-oxazaphospholidines: 1(P=S)–5(P=S). In each case the intermediate tautomeric form 1(P=S)*–5(P=S)*, with an eight-membered ring, is observed. A detailed stereochemical study, based on 1H, 13C, and 31P NMR results is presented for eight compounds: 1–4 and 1(P=S)–4(P=S). In solution we observed the quantitative transformation of 4(P=S) into the corresponding oxo derivative 4(P=O) by the trifluoroacetic anhydride method.