SYNTHESIS IN THE FIELD OF THE ERYTHRINA ALKALOIDS: PART I. THE SYNTHESIS OF HEXAHYDROAPOERYSOTRINE

Abstract

The synthesis of the complete ring system of the aromatic class of Erythrina alkaloids is described. The basic sequence involves reaction of hexahydroindole (whose preparation was studied in some detail) with phenylacetyl chloride to give the ketoamide (VII) which suffered ring closure to the desired ring system (XI) when treated with polyphosphoric acid. Reduction of XI with lithium aluminum hydride gave the corresponding base (XIII). Evidence in support of structure XI is presented. Application of the same sequence with homoveratroyl chloride as starting material led ultimately to the spiroamine (XIV) which proved identical with a sample of natural origin. The stereochemistry of the spiroamines is discussed and the reaction mechanisms involved are critically examined. The new cyclization reaction was successfully applied to the system phenylacetamide–cyclohexanone in an effort to explore its scope.