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Synlett 2011(6): 783-786  
DOI: 10.1055/s-0030-1259920
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Manganese(III)-Catalyzed Formal [3+2] Annulation of Vinyl Azides and β-Keto Acids for Synthesis of Pyrroles

Eileen Pei Jian Ng, Yi-Feng Wang, Shunsuke Chiba*
Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, 637371 Singapore
Fax: +6567911961; e-Mail: shunsuke@ntu.edu.sg;
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Publication History

Received 2 December 2010
Publication Date:
16 March 2011 (online)

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Abstract

Manganese(III)-catalyzed formal [3+2] annnulation of vinyl azides and β-keto acids has been developed for the synthesis of substituted NH pyrroles with a wide range of substituents.

Key words

manganese(III) catalysts - radical reactions - vinyl azides - β-keto acids - pyrroles

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General Procedure for Mn(acac) 3 -Catalyzed Pyrrole Formation from Vinyl Azides and β-Keto Acids: To a solution of α-azido styrene (1a; 52.8 mg, 0.364 mmol) and 2-oxocyclohexanecarboxylic acid (2a; 155.2 mg, 1.09 mmol) in DMF (3.6 mL) was added Mn(acac)3 (12.8 mg, 0.0364 mmol) and the mixture was stirred for 5 h. The reaction mixture was quenched with a pH 9 ammonium buffer, and then extracted with Et2O (2 ×). The combined organic extracts were washed with brine, dried over MgSO4 and concentrated. Purification of the crude product by flash column chromatography (florisil; hexane-EtOAc = 97:3) afforded 3aa (59.5 mg, 0.302 mmol) in 83% yield.