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Synlett 2006(9): 1428-1430  
DOI: 10.1055/s-2006-941559
LETTER
© Georg Thieme Verlag Stuttgart · New York

Reversion of Paal-Knorr Synthesis: A New Strategy for Ring-Opening and N-Substituent Change in 1H-Pyrroles

Rosario Zamora, Francisco J. Hidalgo*
Instituto de la Grasa, Consejo Superior de Investigaciones Científicas, Avenida Padre García Tejero 4, Seville 41012, Spain
Fax: +34(954)616790; e-Mail: fhidalgo@ig.csic.es;
Further Information

Publication History

Received 25 November 2005
Publication Date:
22 May 2006 (online)

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Abstract

1H-Pyrroles were converted into 1,4-dicarbonyl compounds, and then into 1H-pyrroles with a different N-substituent by heating at 110 °C under nitrogen in 0.3 M sodium citrate buffer, pH 3, and in the presence of alkyl or aryl amines. The new pyrroles were obtained in low to very high yields depending upon the pH, the reaction time, the initial pyrrole and amine involved, and the proportion between both reagents.

Key words

amines - cyclizations - pyrroles - ring-closure reactions - ring-opening reactions

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Reactions were carried out by heating at 110 °C under an inert atmosphere, the pyrrole (0.1 mmol) in 3 mL of 0.3 M sodium citrate buffer (pH 3), and in the presence, or not, of the amine (0.1 mmol). The pyrroles produced were extracted three times with CHCl3-MeOH (3:2) and purified by TLC. Identity of purified compounds was confirmed by 1H NMR, 13C NMR and MS.