Exploiting the palladium[0]-catalysed Ullmann cross-coupling reaction in natural products chemistry: Application to a total synthesis of the alkaloid (±)-aspidospermidine

The application of Ullmann cross-coupling reaction for the synthesis of the alkaloid (±)-aspidospermidine was studied. The initial step associated with the second stage of the synthesis of aspidospermidine involved the Pd[0]-catalyzed Ullmann cross-coupling of α-iodoenone with o-iodonitrobenzene. The acid-catalyzed hydrolysis of the last compound and reduction of the resulting aldehyde with sodium borohydride produced higher homologue. Subjection of the last-compound to 1,2-reduction using sodium borohydride gave the expected allylic alcohol which was immediately acetylated under standard conditions to provide the allylic acetate in 96% yield over the two steps.