SYNTHESIS OF AN INTENSELY SWEET CHLORODEOXYSUCROSE: MECHANISM OF 4'-CHLORINATION OF SUCROSE BY SULPHURYL CHLORIDE

Article abstract of DOI:10.1016/0008-6215(87)80200-8

Reaction of 6-acetylsucrose with sulphuryl chloride in chloroform-pyridine affords, after dechlorosulphation and acetylation, a mixture of two isomeric 2,3,6-tri-O-acetyl-4-chloro-4-deoxy-α-D-galactopyranosyl 3-O-acetyl-1,4,6,-trichloro-1,4,6-trideoxy-β-D-hexulofuranosides (6 and 7) and 2,3,6-tri-O-acetyl-4-chloro-4-deoxy-α-D-galactopyranosyl 3,4-di-O-acetyl-1,6-dichloro-1,6-dideoxy-β-D-fructofuranoside (4).Chlorination of C-4, C-1', and C-6' occurs by direct displacement of the initially formed chlorosulphonyloxy groups by chloride ions, but displacement of the 4'-chlorosulphate is sterically hindered.The introdution of a 4'-chloro substituent involves ring opening of intermediate 3',4'-epoxides by chloride ions, the ribo-epoxide producing the sorbo-isomer 6 and the lyxo-epoxide giving the fructo-isomer 7.The proposed mechanism is supported by the formation of 4-chloro-4-deoxyfructofuranosides when 3',4'-lyxo-hexulofuranosides are treated with sulphuryl chloride under the same conditions.