Reduction of 2- and 3-Acylpyrroles. A New Synthesis of the Pyrrolo[1,2-b]cinnolin-10-one Ring System from 1-(4-Methylphenyl)sulfonyl-1H-pyrrole

Reduction of (2-nitrophenyl)(1H-pyrrol-2-yl)methanone 4 with zinc and ammonium chloride gave 5,10-dihydro-pyrrolo[1,2-b]cinnolin-10-one 5 and (2-hydroxylaminophenyl)(1H-pyrrol-2-yl)methanone 6 whereas reduction of 4 with zinc and sodium hydroxide gave only 5. Reaction of (2-nitrophenyl)(1H-pyrrol-3-yl)methanone 10 with zinc and ammonium chloride or zinc and sodium hydroxide afforded (2-nitrosophenyl)(1H-pyrrol-3-yl)methanone 11 and 2-aminophenyl)(1H-pyrrol-3-yl)methanone 12 or 12 as a single product, respectively. Sodium borohydride reduction of (2-nitrophenyl)(1-methyl-1H-pyrrol-2-yl)methanone 13 or (2-nitrophenyl)(1-methyl-1H-3-pyrrolyl)methanone 19 gave a mixture of the corresponding alcohols 15 or 21 and nitroso-ketones 18 or 22. Reduction of alcohols 15 or 21 with zinc and sodium hydroxide afforded nitroso-ketones 18 or 22, respectively.