THE SYNTHESIS OF DIHYDROINDENOINDOLES

The Wender and Bischler indole syntheses have been investigated as potential routes to dihydroindenoindoles. Thus a Wender reaction between N,2-dilithio-N-trifluoroacetylaniline and 2-bromo-5-methoxy-4,6-dimethylindanone affords the corresponding dihydroindeno[1,2-b]indole. In general, however, indolisations of this type are limited to 2-halogenoindanones bearing electron donating groups conjugated with the carbonyl function since these depress enolate anion formation. When such groups are absent the products are N-trifluoroacetylaniline and compounds arising from deprotonation of the 2-halogenoindanones. This problem is offset, but not solved, if the reactions are carried out in the presence of cerium (III) chloride. In a Bischler reaction between 4-methoxyaniline and 2-bromoindanone both 8-methoxydihydroindeno[1,2-b]-indole and 9-methoxydihydroindeno[2,1-b]indole were formed in low yields, together with related pentacyclic compounds.