Cis vicinal diols are converted to olefins using tellurides or selenide reagents. The diol is reacted to convert the hydroxyl groups intogood leaving groups for nucleophilic substitution. Alkyl and aryl sulfonate groups such as mesylate or tosylate are preferred. The productis then reacted with a source of Tc2- or Se2- ions, preferably an alkali metal telluride or selenide, to form the desired olefin. The process isparticularly useful for generating 2',3'- unsaturation in the sugar moiety of nucleosides. Novel intermediate mesylate, tosylate and olefinderivatives of nucleosides are also provided.
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