Transformation of Indole Alkaloids. IV. Reinvestigation of C/D Ring Closing Reaction on Indole Alkaloid Synthesis and the Synthesis of Heteroyohimbines, Aricine and Reserpinine

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Abstract
The C/D ring closing reaction of optically active 2,3-seco-2,3-dihydroakuammigine (II) with Hg(OAc)2-EDTA .cntdot. 2Na was reinvestigated and the isolated products were found to be tetrahydroalstonine, insideheteroyohimbine (V) and insidedehydroyohimbine. There was no evidence for the formation of akuammigine (IV), which was different from that of Uskokovic using racemic compound (II) as the starting material. Modified Polonvski reaction of compound II N-oxide (IXa) gives IV, V, and a piperidine derivative Xb. Bond cleavage between N4 and C5 of compound (II) with carbobenzoxy chloride formed an urethane derivative (Xc) as a major product. Compound Xc yielded a piperidine derivative (Xa) by hydrogenolysis. Pteropodine was transformed to Xa via XIIIc, d. The synthesis of aricine and reserpinine using Xa was achieved by the usual method. Combination of these procedures forms a new general method to synthesize various kinds of aromatic substituted heteroyohimbinoid indole alkaloids.

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