Nitration of Azasydnones and Azasydnonimines: A Method for the Functionalization of Aryl Derivatives

The first example of functionalization of mesoionic 3-R-1,2,3,4-oxatriazol-5-ones and 3-substituted-1,2,3,4-oxatriazol-5-imines (azasydnones and azasydnonimines, respectively) by the electrophilic reaction without destruction of the oxatriazole ring is reported. Nitration of a range of aryl derivatives bearing various electron donating and withdrawing substituents at the ortho-, meta- and para-positions using HNO₃ /H₂ SO₄ mixtures has been assessed in order to develop an approach for the synthesis of corresponding nitroaryl derivatives. Whereas nitration occurs meta to the azasydnone ring, the regioselectivity of the electrophilic substitution can be affected by the nature of the substituent attached to the aryl ring, and a variety of polyfunctionalized derivatives can be readily accessed by using this methodology, which may have applications in the target-oriented synthesis. The reactivity, synthesis, and structure of the mesoionic 3-substituted-1,2,3,4-oxatriazole derivatives described here provide interesting new information on this known but poorly understood heterocycle.