Synthesis 2014; 46(03): 301-306
DOI: 10.1055/s-0033-1340341
paper
© Georg Thieme Verlag Stuttgart · New York

Anomalous Behaviour of cis-Bicyclo[3.3.0]octane-3,7-dione and Its Derivatives During Twofold Fischer Indole Cyclization Using Low-Melting Mixtures

Sambasivarao Kotha*
Department of Chemistry, Indian Institute of Technology, Powai, Mumbai 400 076, India   Fax: +91(22)25727152   Email: srk@chem.iitb.ac.in
,
Ajay Kumar Chinnam
Department of Chemistry, Indian Institute of Technology, Powai, Mumbai 400 076, India   Fax: +91(22)25727152   Email: srk@chem.iitb.ac.in
› Author Affiliations
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Publication History

Received: 30 August 2013

Accepted after revision: 12 November 2013

Publication Date:
17 December 2013 (online)


Abstract

We have developed an efficient method for the synthesis of the pentaleno[2,1-b:5,4-b′]diindole and pentaleno[2,1-b:5,6-b′]diindole skeletons via twofold Fischer indole cyclization. In this new procedure, cis-bicyclo[3.3.0]octane-3,7-dione on treatment with 1-methyl-1-phenylhydrazine in the presence of a low-melting mixture of l-(+)-tartaric acid and N,N′-dimethylurea at 70 °C undergoes a twofold Fischer indole cyclization to deliver the unusual Cs -symmetrical product pentaleno[2,1-b:5,6-b′]diindole, along with the expected C2 -symmetrical pentaleno[2,1-b:5,4-b′]diindole product.

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