A regiospecific fischer indole reaction with 3-oxo-24-nor-allobetulin

Abstract

First case of regiospecific formation of indole fused with a triterpene scaffold is observed. Starting from 3-oxo-24-nor-allobetulin Fischer reaction with phenylhydrazine under the influence of weak acid catalyst led to 3H-indole (indolenine) 4. This process was accompanied by a change in the configuration of the methyl group at C-4 that was confirmed by x-ray diffraction method. On the other hand, 3,2-indole 5 was synthesized under the influence of strong acid catalyst (using phenylhydrazine hydrochloride in AcOH acid or phenylhydrazine in MeOH with a few drops of HCl).