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

Treatment of 1-[(5-chloro-2-nitrophenyl)sulfonyl]-1H-pyrrole-2-carbohydrazi de with powdered iron in glacial acetic acid afforded 1-amino-6-chloro-2-(1 H-pyrrol-2-yl)benzimidazole as the sole product. This compound was also obt ained by iron-acetic acid reduction of 1-(5-chloro-2-nitrophenyl)-1H-pyrrol e-2-carbohydrazide. Splitting of the sulfone group occurred only in the pre sence of the carbohydrazide group. In fact, iron-acetic acid reduction of 5 -chloro-2-nitrophenyl 2-ethoxycarbonyl-1H-pyrrol-1-yl sulfone gave the expe cted 2-amino-5-chlorophenyl 2-ethoxycarbonyl-1H-pyrrol-1-yl sulfone. Treatm ent of this compound with hydrazine yielded the corresponding carbohydrazid e, which failed cyclization when reacted with phosphorus pentoxide. Formati on of 7-chloropyrrolo[1,2-b] [1,2,5]benzothiadiazepin-11(10H)-one 5,5-dioxi de with loss of hydrazine was observed when the above amino hydrazide was r eacted with 2-hydroxypyridine or with glacial acetic acid.