Synthesis of anomerically pure vinyl sulfone-modified pent-2-enofuranosides and hex-2-enopyranosides: a group of highly reactive Michael acceptors for accessing carbohydrate based synthons

Syntheses of the benzyl or the trityl protected α- and β-anomers of vinyl sulfone-modified pent-2-enofuranosides have been initiated by the ring opening of the suitably masked methyl α-lyxofuranosyl-epoxide or methyl β-ribofuranosyl-epoxide or by the nucleophilic displacement of the leaving groups in benzyl protected 3-O-tosyl xylofuranoside and 3-O-mesyl ribofuranoside by p-thiocresol. In case of the latter set of starting materials, α- and β-methyl glycosides formed in almost equal ratio only from the derivatives of d-xylose. For the synthesis of α- and β-anomers of vinyl sulfone-modified hex-2-enopyranosides, a d-glucose derivative was selected over a d-allose derivative as the starting material because the former almost exclusively produced the required methyl pyranosides whereas the latter produced a mixture. All sulfides were converted to vinyl sulfone-modified carbohydrates by the sequential application of oxidation, mesylation and base induced elimination reactions.