Bridged derivatives of sucrose: The synthesis of 6,6′-dithiosucrose, 6,6′-epidithiosucrose, and 6,6′-epithiosucrose

Abstract

Selective iodination and bromination of sucrose at C-6 and C-6′ has been accomplished by reactions with iodine-triphenylphosphine-imidazole and carbon tetrabromide-triphenylphosphine-pyridine, respectively. Substitution of the bromo groups in 6,6′-dibromo-6,6′-dideoxysucrose hexa-acetate by CNS −, AcS −, and Me 2NCS 2 − took place without complications, but when EtOCS 2K was used, a complex reaction sequence took place leading to 6,6′-epithiosucrose hexa-acetate. Similarly, reaction of the dibromo derivative with K 2CS 3 afforded mainly the 6,6′-episulphide together with 6,6′-epidithiosucrose hexa-acetate, which was also formed from the dibromide by sequential treatment with thiourea and sodium metabisulphite. Oxidation of the episulphide with sodium metaperiodate afforded solely the ( R)-sulphoxide, and oxidation with hydrogen peroxide afforded the sulphone. The episulphide, the episulphide S,S-dioxide, and the epidisulphide all showed conformational instability of the ring containing the sulphur atom(s), as indicated by the n.m.r. spectra, but the episulphide S-oxide did not show this behaviour.