Journal of Carbohydrate Chemistry p. 431 - 440 (2001)
Update date:2022-08-29
Topics:
Md. Sofian
Lee, C. Kuan
An unexpected epimerization resulting from the reaction of α-D-glucopyranosyl derivatives with DAST is described. The reaction of 3,4-di-O-acetyl-1,6-di-O-trityl-β-D-fructofuranosyl 2,3,6-tri-O-acetyl-α-D-glucopyranoside (1), methyl 2,3-di-O-acetyl-6-O-trityl-α-D-glucopyranoside (6), 2,3-di-O-acetyl-6-O-trityl-α-D-glucopyranosyl 2,3-di-O-acetyl-6-O-trityl-α-D-glucopyranoside (13), and 2,3-di-O-acetyl-6-O-tert-butyldiphenylsilyl-α-D-glucopyranosyl 2,3,4,6-tetra-O-acetyl-α-D-glucopyranoside (14) with DAST at 0°C did not give the expected C-4 fluorodeoxy galacto derivatives, but instead, the corresponding 4-O-acetyl-3-hydroxy-α-D-galactopyranosides in yields of 52-78%. When the treatment of 6 was carried out at -25°C for ~5 min the corresponding diastereomeric 4-O-diethylaminosulfinates (9a,b) were isolated as the major products (40%). Evidence suggests that the epimerization reaction most probably resulted from an intramolecular displacement of the intermediate diethylaminosulfur difluoride ester or diethylaminosulfinyl ester by the neighbouring acetoxy groups.
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