1-(2-Azirine-2-carbonyl)benzotriazoles: building blocks for the synthesis of pyrrole-containing heterocycles

A one-pot method was developed for the preparation of 2 H -azirine-2-carbonylbenzotriazoles, formed by the reaction of benzotriazole with 2 H -azirine-2-carbonyl chlorides, which were generated by the Fe( ii )-catalyzed isomerization of 5-chloroisoxazoles. The Co( ii )-catalyzed reaction of 2 H -azirine-2-carbonylbenzotriazoles with 1,3-diketones provides 2-((benzotriazol-1-yl)carbonyl)pyrroles in moderate to good yields. Base-promoted annulations of 2-((benzotriazol-1-yl)carbonyl)pyrroles with aldehydes, ketones, isocyanates and isothiocyanates afford various substituted pyrrolo[1,2- c ]oxazole and 1 H -pyrrolo[1,2- c ]imidazole derivatives in moderate to high yields. The 6-acyl group of these adducts can be removed by triflic acid, giving further new pyrrolo-fused O- and N-heterocycles, such as 6-unsubstituted pyrrolo[1,2- c ]oxazol-1(3 H )-one and 1 H -pyrrolo[1,2- c ]imidazole-1,3(2 H )-dione, while the 6-acetyl substituent of 1 H -pyrrolo[1,2- c ]imidazole-1,3(2 H )-dione, when treated with POCl 3 /pyridine, is transformed into the 6-ethynyl substituent. A simple strategy was developed for the synthesis of pyrrole-containing polyheterocycles by sequential annulation of 2 H -azirine-2-carbonylbenzotriazoles derived from 5-chloroisoxazoles.