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Abstract
A general synthesis of the indoloquinolizidine nucleus of the indole alkaloids of the yohimboid and corynanthoid types is based on the partial hydrogenation of the β-(3-indolyl-) ethyl salt of a nicotinic ester (e.g. 1a) and the decarboalkoxylative cyclization of the resultant 1, 4, 5, 6-tetrahydropyridine derivative.3 This scheme necessitates the prior preparation of a nicotinic acid with proper C(4) or C(4)/C(5) substituents and limits the last step to carbon-carbon bond formation between the indole a site and the nicotinic ester C(2) position. The following two-step reaction sequence represents a conceptually alternate strategy of indole alkaloid synthesis, designed especially for the construction of vallesiachotamine (2)4 and involving introduction of a C(4) pyridine substituent in the first step and cyclization at the C(6) pyridine site in the second step of the two-stage operation.