Regioselective synthesis of substituted 1-thiohex-2-enopyranosides

A variety of 1-thiohex-2-enopyranosides have been prepared from their corresponding 3-O-methyl- or 3-O-acetylglycals by using trimethylsilyl thiols catalyzed by BF/sub 3/ etherate. This method is regioselective for thiolation at C-1 in contrast to the same reaction with thiols which produces C-3 products under thermodynamic control. The stereoselectivity of the reaction depended on the choice of trimethylsily thiol and the leaving group at C-3 of the glycal. ((Trimethylsilyl)thio)benzene gave ..cap alpha..-anomers as the only products, whereas (thionacetoxy)trimethylsilane gave more ..beta..-anomer products from 3-O-methylglycals than from 3-O-acetylglycals. Examples reported include the synthesis of S-(2'-pyridyl) 2,3,6-trideoxy-4,6-di-O-acetyl-1-thio-..cap alpha..-D-erythro-hex-2-enopyranoside (1), S-phenyl 2,3,6-trideoxy-4-O-methyl-1-thio-..cap alpha..-L-erythro-hex-2-enopyranoside (15), S-acetyl 2,3,6-trideoxy-4-O-methyl-1-thio-..beta..-L-erythro-hex-2-enopyranoside (16), S-acetyl 2,3-dideoxy-4,6-di-O-methyl-1-thio-..cap alpha..,..beta..-D-erythro-hex-2-enopyranosides (17, 18), S-acetyl 2,3-dideoxy-4,6-di-O-acetyl-1-thio-..cap alpha..,-..beta..-D-erythro-hex-enopyranosides (19, 20), and S-acetyl 2,3,6-trideoxy-4-O-acetyl-1-thiol-..cap alpha..,..beta..-L-erythro-hex-2-enopyranosides (21,22). 24 references, 3 figures, 2 tables.