Effective synthetic routes to activated pyrrolo[3,2,1-hi]indoles

Pyrrolo[3,2,1-hi]indoles have been formed by the aldol cyclisation of 7-formyl-N-indolylacetates. The synthetic sequence incorporates three steps from suitably activated indoles: these are alkylation at nitrogen with a bromoacetic ester, formylation at C7 and an aldol condensation between these two substituents. An X-ray crystal structure of pyrrolo[3,2,1-hi]indole 24 is described.