3,4-anhydro-1,2-O-isopropylidene-beta-D-tagatopyranose and 4,5-anhydro-1,2-O-isopropylidene-beta-D-fructopyranose

3,4-Anhydro-1,2-O-isopropylidene-beta-D-tagatopyranose (8) and 4,5-anhydro- 1,2-O-isopropylidene-beta-D-fructopyranose (10) have been prepared by treat ment of 3,5-di-O-acetyl-1,2-O-isopropylidene-4-O-tolune-p-sulfonyl-beta-D-f ructopyranose with methanolic sodium methoxide. The structures of 8 and 10 were assigned by H-1 and C-13 NMR spectroscopy and that of 10 by X-ray crys tallography; both exist in half-chair conformations. Compounds 8 and 10 int erconvert in aqueous sodium hydroxide, giving a ratio of 1:2 at equilibrium . The monoacetates of 8 and 10 (5-O-acetyl-3,4-anhydro-1,2-O-isopropylidene -beta-D-tagatopyranose and 3-O-acetyl-4,5-anhydro-1,2-O-isopropylidene-beta -D-fructopyranose) undergo stereospecific epoxide ring opening in 80% aceti c acid to give mainly the axial monoacetates 5-O-acetyl-1,2-O-isopropyliden e-beta-D-fructopyranose and 4-O-acetyl-1,2-O-isopropylidene-beta-D-tagatopy ranose, respectively. (C) 2000 Elsevier Science Ltd. All rights reserved.