Synthesis of alkyl and arylthioglycosides and thiodisaccharides via thioiminium salts in a two-phase system

A novel method was developed for the synthesis of alkyl- and arylthioglycosides and thiodisaccharides via glycosylthioiminium salt in a two-phase system using a phase transfer catalyst (PTC). Tetrabutylammonium thiocyanate and tetrabutylphosphonium bromide show a highest efficiency as a PTC for this method. In general, the phosphonium salt is more effective than the ammonium salt as a PTC, and the effect of counter anions of PTC of tetrabutylammonium type is in the order, SCN-> Br-> HSO4-> Cl-. The reactivity of alkyl halide RX is in the order RI > RBr > RCl, independently of the kind of PTC. Using this method, various thioglycosides were prepared in fairly good yields higher than 80%. The reactions proceed easily under mild conditions without a sulfur reagent giving an unpleasant smell. (C) 1999 Elsevier Science B.V. All rights reserved.