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