Synthesis of Substituted 2,6-Dioxabicyclo [3.1.1] Heptanes: 1,3-Anhydro-2,4-DI-O-Benzyl and 1,3-Anhydrq-2,4-DI-O-(p-Bromobenzyl)-β-D-Rhamnopyranose

Abstract

Abstract The title compounds were synthesized from D-mannose in 11 steps, most of which were carried out readily in high yield. 6-Deoxygenation of methyl 2,3-O-isopropylidene-6-O-(p-tolylsulfonyl)-α-D-mannopyranoside (5) and methyl 4-O-(p-bromobenzyl) -2,3-O-isopropylidene-6-O-(p-tolylsulfonyl)-α-D-mannopyranoside (13) was carried out smoothly by direct reduction with lithium aluminum hydride in oxolane. The key intermediates for ring closure were 3-O-acetyl-2,4-di-O-benzyl- (11) and 3-O-acetyl-2,4-di-O-(p-bromobenzyl)-α-D-rhamnopyranosyl chloride (18) that were prepared by direct chlorination of the corresponding methyl rhamnopyranosides with hydrogen chloride in diethyl ether. Ring closure of the chlorides was conducted with potassium tert-butoxide in oxolane at room temperature in high yield. The 1,3-anhydro-β-D-rhamnopyranose derivatives were characterized from their 1H NMR, MS, and IR spectra, and by optical rotations and elemental analyses.