ChemInform Abstract: Synthesis of Carbazoles Related to Carbazomycin, Hyellazole and Ellipticine.

ChemInform Abstract

The reaction of the 2-alkylsubstituted indoles (I) with 2,3-unsaturated ketones of type (II) yields the desired carbazoles (III). In some cases the yields can be slightly improved by addition of molecular sieves as is shown for the reaction of (Ia) with the cyclic ketone (IV). The 5H-benz(b)carbazoles (VI), which are formed as by-products in the presence of molecular sieves, represent deaza analogues of ellipticine. Attempts to synthesize 4-methoxysubstituted carbazoles, analogues of carbazomycin and hyellazole, fail since the methoxy group is lost during the reaction. A second way to carbazoles is based on the reaction of the 2-vinylic indoles (IX) with the Vilsmeier reagent. The results, however, are not very promising since only (IIIa) (R1: -H) can be obtained in an acceptable yield. Further attempts to convert (IX) to carbazoles are unsuccessful. The synthesis of (IXa) by Fischer indolization using PPA is also applied to the preparation of the carbazole (XII) from phenylhydrazine (VII) and Hagemann's ester thus circumventing a multi-step sequence starting from 2-(2-tosyloxyethyl)indole and ethyl acetoacetate.