Moffatt oxidation of 2',3'-O-isopropylideneuridine (1a) and treatment of the crude 5'-aldehyde with formylmethylene-stabilized Wittig reagent gave the vinylogously extended 7'-aldehyde2a. Condensation of 2a with ethoxycarbonyl- or dibromomethylene phosphorane reagents gave the conjugated dienes 6a and 4a, respectively. Deacetonization gave diene ester 7a [5'(E),7'(E); with s-trans conformation] and dibromodiene 5a [5'(E)], respectively.
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