Indole alkaloid synthesis

Indole acetic acid and methyl 1,4,5,6-tetrahydronicotinylacetate obtained by hydrogenation of methyl nicotinylacetate were combined in the presence of base to yield methyl 1-(3-indoleacetyl)-1,4,5,6-tetrahydronicotinylacetate in 45% yield. This, upon heating in polyphosphoric acid, yielded in 73% 2-deethyl-5,17-diketo-2,16-dihydrovincadifformine with complete stereospecific formation of all five chiral centers. Reduction of the two keto functions led to 2-deethyl-2,16-dihydrovincadifformine, whereas reduction of the lactam and oxidation of the 2,16 carbon-carbon bond yielded 2-deethyl-16-ketovincadifformine. 16 ketopseudovincadifformine was prepared in the same manner starting from methyl 5-ethyl-nicotinylacetate