Synthesis of Vinca Alkaloids and Related Compounds. 63. A New Synthetic Pathway for Preparing Alkaloids and Related Compounds with the Aspidosperma Skeleton. Total Syntheses of (+/-)-Vincadifformine, (+/-)-Tabersonine, and (+/-)-3-Oxotabersonine

Article abstract of DOI:10.1021/jo00058a025

Compound 3, which has an indole skeleton containing a masked acryl ester function, was synthesized from the hydrochloride of (2-ethoxycarbonyl)tryptamine (2).The cycloaddition of 3 with methyl 4-formylhexanoate (21) or with 5-(benzoyloxy)-2-ethylpentanal (33) yielded the starting materials for target compounds (+/-)-vincadifformine (4), (+/-)-3-oxotabersonine (42), and (+/-)-tabersonine (43).The synthesis of vincadifformine (4) was achieved in two different ways: via 3-oxovincadifformine (7) and via tricyclic benzoate esters 37 and 38.The double bond required in tabersonine (43) and 3-oxotabersonine (42) was introduced by treatment of 3-thioxovincadifformine (39) with p-toluenesulfinyl chloride.