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Paper | Regular issue | Vol 53, No. 10, 2000, pp.2163-2174
Published online, 1st January, 1970
DOI: 10.3987/COM-00-8970
Reductive Smiles Rearrangement of 1-[(5-Chloro-2-nitrophenyl)sulfonyl]-1H-pyrrole-2-carbohydrazide to 1-Amino-6-chloro-2-(1H-pyrrol-2-yl)benzimidazole

Romano Silvestri, Augusto Pifferi, Gabriella De Martino, Silvio Massa, Carmela Saturnino and Marino Artico*

*Istituto Pasteur-Fondazione Cenci Bolognetti, Dipartimento di Studi Farmaceutici, Università di Roma “La Sapienza”, BOX 36 - ROMA 62, Piazzale Aldo Moro 5, 00185 Roma, Italy

Abstract

Treatment of 1-[(5-chloro-2-nitrophenyl)sulfonyl]-1H-pyrrole-2-carbohydrazide with powdered iron in glacial acetic acid afforded 1-amino-6-chloro-2-(1H-pyrrol-2-yl)benzimidazole as the sole product. This compound was also obtained by iron-acetic acid reduction of 1-(5-chloro-2-nitrophenyl)-1H-pyrrole-2-carbohydrazide. Splitting of the sulfone group occurred only in the presence of the carbohydrazide group. In fact, iron-acetic acid reduction of 5-chloro-2-nitrophenyl 2-ethoxycarbonyl-1H-pyrrol-1-yl sulfone gave the expected 2-amino-5-chlorophenyl 2-ethoxycarbonyl-1H-pyrrol-1-yl sulfone. Treatment of this compound with hydrazine yielded the corresponding carbohydrazide, which failed cyclization when reacted with phosphorus pentoxide. Formation of 7-chloropyrrolo[1,2-b] [1,2,5]benzothiadiazepin-11(10H)-one 5,5-dioxide with loss of hydrazine was observed when the above amino hydrazide was reacted with 2-hydroxypyridine or with glacial acetic acid.