Spiroindimicin model studies reveal a facile route to cyclopenta[c]pyrazoles

Abstract

Synthesis of the spirobisindole core of the [5,5]-spiroindimicin alkaloids by Fischer indolisation between a cyclopenta[b]indole-3-carbaldehyde and phenylhydrazine did not proceed as anticipated, instead forming a cyclopenta[c]pyrazole. Further investigation revealed this unusual rearrangement reaction shows good scope and comprises a straightforward method to access this heteroaromatic motif.