Synthesis and properties of 2,3-anhydro-D-mannose and 3,4-anhydro-D-altrose

Abstract

Treatment of benzyl 3,4,6-tri-O-acetyl-2-O-p-tolylsulphonyl-β-D-glucopyranoside (5) with sodium methoxide in methanol gave benzyl 2,3-anhydro-β-D-mannopyranoside (7)(65%) and benzyl 3,4-anhydro-β-D-altropyranoside (8)(29%). Hydrogenolysis of the glycoside (7) in tetrahydrofuran over palladium–charcoal yielded crystalline 2,3-anhydro-β-D-mannopyranose (9) which, in aqueous solution, rapidly underwent mutarotation to give an equilibrium mixture containing the α-pyranose (10)(23%), the β-pyranose (9)(7%), the α-furanose (12)(65%), and the β-furanose (11)(5%), whose composition was determined by g.l.c., g.l.c.–mass spectrometry, and n.m.r. spectroscopy; the assignment of anomeric configuration to the furanose isomers rests on conformational arguments. A similar mixture was obtained by hydrogenolysis of benzyl 2,3-anhydro-α-D-mannopyranoside (13). Hydrogenolysis of the glycoside (8) in methanol gave an equilibrium mixture of the α- and β-forms [(14) and (15)] of 3,4-anhydro-D-altropyranose (32.5 and 67.5%, respectively).