The Pschorr cyclization. A novel Pschorr reaction with a pyrrole derivative: synthesis of a pyrrolo[1,2-c]quinazoline and a new route to arylpyrroles

Abstract

The copper-catalysed decomposition of the diazonium chloride derived from N-(3,5 -diethoxycarbonyl -4-methylpyrrol-2-ylmethyl)-N-methanesulphonyl-o-phenylenediamine (2) gave spiro[l-methanesulphonyl - 3H-indoline - 3,2'- (3', 5'- di-ethoxycarbonyl-4-methyl-2'H-pyrrole)] (4), in high yield. However, thermal decomposition of the diazonium chloride gave 2,4-diethoxy-carbonyl-5-(N-methanesulphonyl-o-aminophenyl)-3-methylpyrrole (3) as the major product. The spiro compound (4) afforded the phenylpyrrole (3) in almost quantitative yield on treatment with concentrated hydrochloric acid, while 100% phosphoric acid or 60% sulphuric acid converted the spiro compound (4) into 1,3-diethoxycarbonyl-5-methanesulphonyl-2-methyl-4,5-dihydropyrrolo[1,2-c]quinazoline (12). The latter reaction could also be achieved thermally. Analytical and spectral data are presented which support the structures proposed.