<i>N</i>-Phenyl-1,2,4-triazoline-3,5-dione (PTAD) as a Dienophilic Dinitrogen Equivalent: A Simple Synthesis of 3-Amino-1,2,4-benzotriazines from Arylcarbodiimides
N-Arylcarbodiimides react with PTAD to provide [1,2,4]triazolo[1,2-a][1,2,4]benzotriazines by a [4+2] cycloaddition reaction. When asymmetrically substituted diarylcarbodiimides are used, the cycloaddition proceeds with total chemoselectivity because only the more electron-rich aryl nucleus is involved. This observation has been rationalized by a computational study using DFT methods that shows that