Synthesis and Conformation of Substituted 2,6-Dioxabicyclo[3.1.1]Heptanes: 1,3-Anhydro-6-Azido-2,4-Di-O-Benzyl-6-Deoxy- And 1,3-Anhydro-6-Azido-2,4-Di-O-(P-Bromobenzyl)-6-Deoxy-β-D-Mannopyranose

ABSTRACT Methyl 6-azido-4-O-benzyl-6-deoxy- (5) and methyl 6-azido-4-O- (p-bromobenzyl)-6-deoxy- α-D -mannopyranoside (6) were obtained by reaction of methyl 4-O-benzyl- (1) and methyl 4-O-(p-bromobenzyl)- 2,3-O-isopropylidene-6-O-toluene-sulfonyl-α-D-mannopyranoside (2) with sodium azide, followed by acid hydrolysis. Selective benzylation and p-bromobenzylation of 5 and 6 under phase transfer conditions afforded methyl 6-azido-2,4-di-O-benzyl-6-deoxy- (7) and methyl 6-azido-2,4-di-O-(p-bromobenzyl)-6-deoxy-α-D-mannopyranoside (8) respectively, which were acetylated and subsequently chlorinated to give 3-O-acetyl-6-azido-2,4-di-O-benzyl-6-deoxy- (11) and 3-O-acetyl-6-azido-2,4-di-O-(p-bromobenzyl)-6-deoxy-α-D-mannopyranosyl chloride (12). Ring closure of 11 and 12 was conducted in the presence of potassium tert-butoxide to give the title anhydro sugar ethers in almost quantitative yield. The full assignments of 1H and 13C NMR spectra of the anhydro sugar ethers were achieved by single frequency decoupling...