Active manganese dioxide promoted cyclization of ortho-(1H-pyrrol-1-yl)aryl and heteroaryl carboxylic acids to 5H-pyrrolo[1,2-a][3,1]benzoxazin-5-one derivatives

The hitherto unknown lactone 5H-pyrrolo[1,2-a][3,1]benzoxazin-5-one and six of its substituted derivatives have been prepared by active manganese dioxide promoted oxidative cyclization of the corresponding 2-(1H-pyrrol-1-yl)benzoic acids, under mild conditions, in moderate yields. The method was successfully extended to the cyclization of some ortho-(1H-pyrrol-1-yl)heteroaryl carboxylic acids and 2-(1H-indol-1-yl)benzoic acids.

The cyclization of various 2-(1H-pyrrol-1-yl)benzoic acids to 5H-pyrrolo[1,2-a][3,1]benzoxazin-5-one derivatives was obtained by the oxidative action of active MnO2 in 20-71% yield, under mild conditions.