The 4,6:4′,6′-dibenzylidene acetal of α,α-trehalose has been converted into the three possible 2,3:2′,3′-diepoxides: the symmetrical allo, allo- and manno, manno-isomers, and the non-symmetrical allo, manno-isomer. These di-epoxides were prepared, respectively, by the action of sodium ethoxide on the 2,3,2′,3′-tetramesylate, the 2,2′-ditosylate, and the 2,3,2′-tritosylate of the dibenzylidene acetal, the latter two esters being prepared by selective tosylation. Selective monotosylation of the dibenzylidene acetal afforded the 2-monotosylate in moderate yield, which was converted into the monoepoxide, namely 2,3-anhydro-4,6-O-benzylidene-α-D-mannopyranosyl 4,6-O-benzylidene-α-D-glucopyranoside by the action of base. The action of base on the dimesylate ester of the monoepoxide gave the non-symmetrical manno, allo-diepoxide. Extensive use was made of H n.m.r. spectroscopy for the structural elucidation of these products.