A rationale for the study of 1,3-anhydroglycopyranoses was given previously in an article that described the synthesis of 1,3-anhydro-L-rhamnopyranose derivatives'. Earlier, 1 ,3-anhydro-D-gh.tco-2~3 and -manno-pyranose4.5 derivatives had been reported by Schuerch and collaborators. In the present communication, we report the synthesis and conformation of 1,3-anhydro-2,4,6-tri-0-benzyl-P_Dgalactopyranose, which is of interest because its stereoregular polymerization and then deprotection can afford an a-(1+3)-linked D-galactopyranan, a useful model compound for immunology research.
Methyl cu-D-galactopyranoside (l), prepared from D-galactose according to a reported method6, was selectively 3-mono-0-allylated as the dibutyltin complex, following the method used for the preparation of ally1 3-O-crotyl-a-o-galactopyranoside', to afford methyl 3-0-allyl-cr-D-galactopyranoside (2). Compound 2, a readily crystallized compound after purification by column chromatography, was converted into the corresponding 2,4,6-tri-O-benzylated derivative (3) in the conventional way. Hydrolysis of 3 under acidic conditions gave 3-O-allyl-2,4,6-tri-Obenzyl-D-galactopyranose (7). Rearrangement of the ally1 group to a propenyl group with tris(triphenylphosphine)chlororhodium furnished 2,4,6-tri-O-benzyl-3-0-propenyl-D-galactopyranose (8) that was converted, without isolation into 2,4,6tri-0-benzyl-D-galactopyranose (9) under slightly acidic conditions. Acetylation with acetic anhydride-pyridine gave the 1,3-diacetate (10) quantitatively. 3-0-Acetyl-2,4,6-tri-0-benzyl-a-D-galactopyranosyl chloride (11) was obtained quantitatively from compound 10 with hydrogen chloride in ether by the method of *Project supported by the National Natural Science Foundation of China.