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

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.& COPY; 2023 Elsevier Ltd. All rights reserved.

Automated summary

The synthesis of the spirobisindole core of the [5,5]-spiroindimicin alkaloids through Fischer indolisation between a cyclopenta[b]indole-3-carbaldehyde and phenylhydrazine did not proceed as expected, resulting in the formation of a cyclopenta[c]pyrazole instead. Further investigation revealed that this unusual rearrangement reaction has a wide range of applications and provides a straightforward method to access this heteroaromatic motif.