Catalytic Oxidation of N-Phenylamidrazones to 1,3-Diphenyl-1,4-dihydro-1,2,4-benzotriazin-4-yls: An Improved Synthesis of Blatter's Radical

Blatter's radical, 1,3-diphenyl-1,4-dihydro-1,2,4-benzotriazin-4-yl (1a, R = H), and several of its C-7 substituted analogues (R = CF3, Cl, Br, I, Me, OMe) were prepared in good-to-excellent yields through catalytic oxidation of the corresponding amidrazones by using palladium-on-carbon (1.6 mol%) and 1,8-diazabicyclo[5.4.0]undec-7-ene (0.1-1.0 equiv) in air. The reaction conditions were suitable for the preparation of Blatter's radical on a one-gram scale in up to 87% yield.