TOTAL SYNTHESIS OF THE INDOLE ALKALOIDS DL-EBURNAMONINE AND DL-VINCAMINE

High yield total syntheses of racemic eburnamonine (1) and vincamine (2) are described. These syntheses utilize the tricyclic lactam 3 as a common intermediate. The latter compound is convergently prepared from tryptamine hydrochloride and 5-bromo-2-ethylvaleryl chloride. The lactam 3 is transformed via its dianion 4 into eburnamonine (1) by reaction with methyl bromoacetate followed by Bischler cyclization. Reduction of the resulting imine salt and subsequent lactamization afford I in 65% overall yield. Vincamine (2) is prepared by reaction of dianion 4 with methyl-2-methylthioacrylate. Bischler cyclization, imine reduction, and oxidative cyclization stereospecifically afford 2 in 40% overall yield. © 1979, American Chemical Society. All rights reserved.