Synthesis of Vinca Alkaloids and Related Compounds. 90. New Results in the Synthesis of Alkaloids with the Aspidospermane Skeleton. First Total Synthesis of (±)-3-Oxominovincine

The tryptamine derivative 1 readily reacted with methyl 4-acetyl-5-bromopent-4-enoate (9) that had been built up from 2,4-pentanedione. On intramolecular dehydration and subsequent [4 + 2] cycloaddition, the reaction product 10 gave the epimers 12 and 13 having the d-secoaspidospermane skeleton. Compound 12 directly and 13 after epimerization yielded (±)-3-oxominovincine (14). Regioselective reduction of 14 furnished (±)-minovincine (17).