GENERAL METHODS OF SYNTHESIS OF INDOLE ALKALOIDS - 14. SHORT ROUTES OF CONSTRUCTION OF YOHIMBOID AND AJMALICINOID ALKALOID SYSTEMS AND THEIR 13C NUCLEAR MAGNETIC RESONANCE SPECTRAL ANALYSIS.

Article abstract of DOI:10.1021/ja00428a044

Conceptually new schemes of synthesis of indole alkaloids are introduced. The yohimboid ring system is constructed by the sequential treatment of 1-tryptophyl-3-( beta -ketobutyl)pyridinium bromide with base and acid. Hydrogenation of the product yields d,l-pseudoyohimbone. The ajmalicinoid ring system is formed by the exposure of 1-tryptophyl-3-acetylpyridinium bromide to sodio dimethyl malonate and then to acid, followed by hydrogenation. Subsequent reduction and dehydration of the products lead to the racemates of the alkaloids tetrahydroalstonine and akuammigine as well as isomers of ajmalicine. Shifts of specific carbons are found to be of stereochemically diagnostic value.