Cation-Exchange resin-catalyzed addition of methanol to benzoylated 1,5-anhydro-2-deoxy-d-hex-1-enitols

1,5-Anhydro-3,4,6-tri-O-benzoyl-2-deoxy-d-arabino-hex-1-enitol (1) was boiled under reflux with methanol and AG 50W-X8 cation-exchange resin. A two-product mixture of glycosides (2 and 3) was obtained in 38% yield, together with 19% of unreacted material. 1,5-Anhydro-3,6-di-O-benzoyl-2-deoxy-d-arabino-hex-1-enitol (7) was prepared from 1,5-anhydro-2-deoxy-d-arabino-hex-1-enitol by selective benzoylation, from which the corresponding 4-methanesulfonate 8 was obtained. Treatment of 8 with sodium benzoate in hexamethylphosphoric triamide for 72 h at 100° afforded 1,5-anhydro-3,4,6-tri-O-benzoyl-2-deoxy-d-lyxo-hex-1-enitol (9) in 52% yield. An unknown byproduct (B), tentatively shown to be a tri-O-benzoyl-d-hex-2-enopyranose analog, was also isolated in 14% yield. The 270-MHz n.m.r. spectrum of B was analyzed in terms of its J_1,3, J_2,4, and J_4,5 coupling constants in relation to the various configurational and conformational possibilities for hex-2-enopyranoses, and was identified as 1,4,6-tri-O-benzoyl-2,3-dideoxy-α-d-threo-hex-2-enopyranose having the ^oH₅ conformation. The analysis presented should also be applicable to pent-2-enopyranose systems. When 9 was treated with methanol in the presence of AG 50W-X8 cation-exchange resin, a mixture of glycosides 4 and 5 was obtained in 47% yield. The low yields were attributed to methanolysis of the benzoyl groups during the reaction.