TfOH-promoted synthesis of 4,5-dihydrooxazolo[5,4- c]isoquinolines via formal [3 + 2] cycloaddition of 4-diazoisoquinolin-3-one and benzonitriles

A facile and efficient method for the synthesis of novel 2-substituted 4-tosyl-4,5-dihydrooxazolo[5,4-c]isoquinolines from 4-diazoisoquinolin-3-ones and nitriles is reported. The reaction proceeded through a TfOH-promoted formal [3 + 2] cycloaddition and the products could be conveniently converted to 2-aryloxazolo[5,4-c]isoquinolines and the subsequent 2-(oxazolo[5,4-c]isoquinolin-2-yl)phenol which emitted bright green light in dilute dichloromethane solution and in solid form as well. Simple operation, metal-free and mild reaction conditions, short reaction time and broad substrate scope are the prominent features of this methodology.