A rapid and efficient synthesis of 2H-indazoles has been developed, which involves the [3+2] dipolar cycloaddition of arynes and sydnones. The process proceeds under mild reaction conditions in good to excellent yields.

A rapid and efficient synthesis of 2H-indazoles has been developed using a [3 + 2] dipolar cycloaddition of sydnones and arynes. A series of 2H-indazoles have been prepared in good to excellent yields using this protocol, and subsequent Pd-catalyzed coupling reactions can be applied to the halogenated products to generate a structurally diverse library of indazoles.

N-Unsubstituted β-lactams react with a molecule of aryne by insertion into the amide bond to form a 2,3-dihydroquinolin-4-one, which subsequently reacts with another molecule of aryne to form an acridone by extrusion of a molecule of ethylene. 2,3-Dihydroquinolin-4-ones react under the same reaction conditions to afford identical results. This is the first example of ethylene extrusion in aryne chemistry.

A study of the nucleophilic addition of amines to 2,3-pyridyne has been carried out. 2-Aminopyridines have been generated exclusively. A series of benzonaphthyridinones have been synthesized by reacting 2,3-pyridyne and o-aminobenzoates.