Asymmetric synthesis. Part II. Stereospecific synthesis of benzylic centres. Some 6-deoxy-5-C-phenylhexose derivatives

Abstract

Asymmetric benzylic centres are introduced into carbohydrate molecules by stereospecific or highly stereoselective reactions. The absolute configurations of these benzylic centres are established by n.m.r. spectroscopy. 6-Deoxy-1,2,-O-isopropylidene-5-C-phenyl-β-L-idofuranose and 1-deoxy-3,4:5,6-di-O-isopropylidene-2-C-phenyl-D-glucitol are prepared by the stereospecific reaction of methylmagnesium iodide with 1,2-O-isopropylidene-5-C-phenyl-α-D-xylo-pentodialdofuranose and 2,3:4,5-di-O-isopropylidene-1-C-phenyl-D-arabino-pentose respectively. 6-Deoxy-1,2-O-isopropylidene-5-C-phenyl-α-D-glucofuranose and 1-deoxy-3,4:5,6-di-O-isopropylidene 2-C-phenyl-D-mannitol are the preponderant products from the reaction of phenylmagnesium bromide with 6-deoxy-1,2-O-isopropylidene-α-D-xylo-hexosulofuranose and 1-deoxy-3,4:5,6-di-O-isopropylidene-L-arabino hexulose respectively. Suitable cyclic derivatives of these compounds are prepared in order to relate the configuration of the benzylic centre to the known configurations of the other asymmetic centres.