Diastereoselective synthesis of spiro[carbazole-3,5′-pyrimidines] and spiro[carbazole-3,1′-cyclohexanes] via four-component reaction

Abstract

Functionalized spiro[carbazole-3,5′-pyrimidines] and spiro[carbazole-3,1′-cyclohexanes] were efficiently synthesized in satisfactory yields with high diastereoselectivity by CuSO₄ catalyzed multicomponent reaction of indole-2-acetate, aromatic aldehyde and 1,3-dimethylbarbituric acid or dimedone. The reaction was finished with sequential Diels–Alder reaction of both in situ generated indole-2,3-quinodimethane and a dienophile. Additionally, the initially formed spiro[carbazole-3,5′-pyrimidines] were converted to dehydrogenated spiro[carbazole-3,5′-pyrimidines] by DDQ oxidation. The initially formed spiro[carbazole-3,1′-cyclohexanes] were converted to δ-valerolactone-substituted carbazoles by a DDQ promoted Baeyer–Villiger oxidation process.