Isothiazoles. Part IV. Cycloaddition reactions of diaryl-oxazolones and munchnones to 3-diethylamino-4-(4-methoxyphenyl)-isothiazole 1,1-dioxide: A new synthesis of triarylpyrroles

3-Diethylamino-4-(4-methoxyphenyl)-isothiazole 1,1-dioxide (3) readily reacts with oxazolones 2 and munchnones 7 affording with satisfactory yield 3-diethylamino-4,6-diaryl-3a,4-dihydro-3a-(4-methoxyphenyl)-6aH-pyrrol o[3,4-d]isothiazole 1,1-dioxides 4 and 3-diethylamino-4,6-diaryl-5-alkyl-3a-(4-methoxyphenyl)-pyrrolo[3,4-d]i sothiazole 1,1-dioxides 8, respectively. The behaviour of the cycloadducts towards elevated temperatures and/or basic conditions was investigated. Under these conditions the primary products lost SO2 and diethylcyanamide affording 1-alkyl-2,3,5-triarylpyrroles 9 and 1H-2,3,5-triarylpyrroles 10. These latter were found to be better obtained through thermal decompression of N-protected cycloadducts 8 and subsequent deprotecting the final pyrroles.