Synthesis of thiospiroacetals. X-Ray crystal structure determinations for (7RS,11RS)-1,4,8-trioxa-13-thiadispiro[4.1.5.3]pentadecan-11-ol and (4RS,6SR)-4-p-nitrobenzoyloxy-1,7-dithiaspiro[5.5]undecane

Abstract

Deprotonation of 2-phenylthiotetrahydrothiopyran 10 and addition of the epoxide 14 gave the 2-alkyl-tetrahydrothiopyrans 16a, b. Deprotection, followed by cyclisation using silver nitrate and triethylamine in aqueous acetonitrile, gave the monothiospiroacetals 18 and 19(93%), ratio 67:33. The monothiospiroacetals 29 and 30 were similarly obtained from 2-phenylthiotetrahydrothiopyran 26. The formation of dithiospiroacetals from 2-phenylthiotetrahydrothiopyrans was inefficient. However, the 2H-3,4-dihydrothiopyran 25 was alkylated using epoxides 14 and 56, and the products converted into the dithiospiroacetals 48 and 50, and 62 and 63, respectively. The 2H-dihydrothiopyran 65 was similarly alkylated using the epoxide 14, and the product taken through to provide the dithiospiroacetal 71. In each case the major product was that expected on the basis of the anomeric effect. The structures of (7RS,11RS)-1,4,8-trioxa-13-thiadispiro[4.1.5.3]pentadecan-11-ol 18 and the p-nitrobenzoyloxydithiospiroacetal 49, were established by X-ray crystallography.