Stereoselective ring-opening of acetylated pyranose-1,2-(ethyl orthoacetates)

Article abstract of DOI:10.1248/cpb.41.90

When acetylated pyranose-1,2-(ethyl orthoacetates) were hydrolyzed in acidic solvents, the ring-opening of the orthoacetate rings was influenced by the axial or equatorial OAc group at C-4 on the pyranoses; on acid-catalyzed hydrolysis, 3,4,6-tri-O-acetyl-α-D-galactopyranose- (8) and methyl 3,4-di-O-acetyl-α-D-galacturonatopyranose-1,2-(ethyl orthoacetate) (16) having an axial OAc group at C-4 on the pyranose rings gave 1,3,4,6-tetra-O-acetyl-α-D-galactopyranose (9) and methyl 1,3,4-tri-O-acetyl-α-D-galacturonatopyranose (23), respectively, whereas 3,4,6-tri-O-acetyl-α-D-glucopyranose- (10) and methyl 3,4-di-O-acetyl-α-D-glucuronatopyranose-1,2-(ethyl orthoacetate) (22) having an equatorial OAc group at C-4 on the pyranose rings gave 2,3,4,6-tetra-O-acetyl-D-glucopyranose (11) and methyl 2,3,4-tri-O-acetyl-D-glucuronatopyranose (24), respectively. On the acid-catalyzed hydrolysis, 3,4-di-O-acetylβ-L-arabinopyranose-1,2-(ethyl orthoacetate) (34) having an axial OAc group at C-4 on the pyranose ring gave a mixture of 1,3,4-tri-O-acetyl-β-L- (35) and 2,3,4-tri-O-acetyl-L-arabinopyranose (36). These selectivities of ring-opening of the 1,2-(orthoacetates) were considered to have resulted from the differences of the conformers of the 1,2-(orthoacids) intermediates derived from the 1,2-(orthoacetates) and the orientation of the acetyl groups at C-4 on the pyranose rings.

Full text of DOI:10.1248/cpb.41.90

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