Syntheses of novel glycosylidene-spiro-heterocycles related to hydantocidin

Reaction of 2,3,4,6-tetra-O-acetyl-1-bromo-1-deoxy-beta-D-galactopyranosyl cyanide (4) with thiocyanate ions results in the formation of both anomers of per-O-acetylated 1-deoxy-1-thiocyanato-D-galactopyranosyl cyanides (5a a nd 5b). The thiocyanate group in these products is resistant to isomerizati on into isothiocyanate even at elevated temperatures. The X-ray structure o f 5a is consistent with the operation of an exo-anomeric effect for the thi ocyanate group. Compounds 5a and 5b react with hydrogen sulfide under mild conditions to yield galactopyranosylidene-spiro-thiazolidine (8) and -thiaz oline (9, 12, and 13) derivatives. (C) 1999 Elsevier Science Ltd. All right s reserved.