Regiospecific preparation of γ-carbolines and pyrimido[3,4-a]indole derivatives by intramolecular ring-closure of heterocumulene-substituted indoles

Article abstract of DOI:10.1016/0040-4020(96)00213-X

Compounds resulting from the aza-Wittig reaction of iminophosphorane derived from 2-(2-azidoethyl)indole and carbon disulfide, diphenylketene, aldehydes and acyl chlorides undergo ring-closure under acidic, basic and thermal conditions to give either dihydro γ-carbolines or dihydropyrimido[3,4-a]indoles in a completely regiospecific fashion. The mode of cyclization strongly depends on the cyclizating agents as well as the nature of the reagent. The related carbodiimides 9 undergo regiospecific cyclization to give dihydropyrimido[3,4-a]indoles under acidic, basic or thermal conditions.