When irradiated with u.v. light, methanolic solutions of fully protected 2,3- and 3,4-O-o-nitrobenzylideneglycopyranosides rearrange to give the corresponding glycoside o-nitrosobenzoates. Oxidation of these products with trifluoroperacetic acid gives glycoside o-nitrobenzoates. Since each of these transformations gives almost exclusively one isomer in high yield, the reactions constitute a good synthesis of partially protected pyranose derivatives.

The 2,3-O-o-nitrobenzylidene derivatives [(1) and (7)] of methyl 4-O-acetyl-α-L-rhamnoside and methyl 4,6-di-O-methyl-β-D-alloside gave respectively the 2- and the 3-o-nitrobenzoates [(3) and (9)]. The 3,4-O-o-nitrobenzylidene derivatives (10) and (16) of methyl 2-O-acetyl-α-L-fucoside and methyl 2-O-acetyl-β-L-arabinoside gave the 4-O-o-nitrobenzoyl derivatives (12) and (18), and the corresponding derivative (13) of 1,6-anhydro-2-O-mesyl-β-L-galactose gave the 3-O-o-nitrobenzoyl derivative (15). In all the reactions the minor positional isomer constituted less than 5 % of the total product. The 3-O-o-nitrobenzoyl-rhamnoside (5) and -arabinoside (20) were the only ones detectable by n.m.r. spectroscopy.

Oxidation of the o-nitrobenzoates (3) and (18) with ruthenium tetraoxide afforded methyl 4-O-acetyl-6-deoxy-2-O-o-nitrobenzoyl-α-L-arabino-hexopyranoside-3-ulose (6) and methyl 2-O-acetyl-4-O-o-nitrobenzoyl-β-L-threo-pentopyranoside-3-ulose (21), respectively.