Nucleophilic displacement-reactions of the 4-sulfonyloxy group in derivatives having the D-manno configuration

Article abstract of DOI:10.1016/0008-6215(91)80099-9

Methyl 2,3-di-O-benzoyl-6-deoxy-4-O-(p-tolylsulfonyl) and 4-O-<(p-nitrophenyl)sulfonyl>-α-D-mannopyranosides (9 and 10) were prepared by three different routes from methyl α-D-mannopyranoside (1).The analogous 4-sulfonyloxy derivatives having HO-2 and HO-3 free (14 and 15) were also synthesized from 1.Nucleophilic substitution of the sulfonyloxy group of 9, 10, 14, and 15 by potassium thiocyanate in N,N-dimethylformamide was attempted.Compounds 9 and 10 gave a mixture of solvolysis products: methyl 2,3-di-O-benzoyl-6-deoxy-α-D-talopyranoside (17), methyl 3,4-di-O-benzoyl-6-deoxy-α-D-talopyranoside (18), and methyl 2,4-di-O-benzoyl-6-deoxy-α-D-talopyranoside (19), which are evidently formed by intramolecular displacement of the 4-sulfonate by backside attack of the C-2 benzoyloxy substituent, followed by benzoyl migration.The structure of compounds 17-19 was established by spectroscopic analysis, and then chemically confirmed.Although compound 14 decomposed during the substitution reaction, the 4-p-nitrophenylsulfonyl derivative 15 gave a 2:1 mixture of the 4-thiocyano derivatives with inversion and retention of the C-4 configuration.