4-Phenyl-1,2,4-triazoline-3,5-dione (PTAD) is an azodicarbonyl compound. PTAD is one of the strongest dienophiles and reacts rapidly with dienes in Diels-Alder reactions.[1] The most prominent use of PTAD was the first synthesis of prismane in 1973.[2]
The compound was first synthesized in 1894 by Johannes Thiele and . The oxidation of 4-Phenylurazole with lead tetroxide in sulfuric acid yielded small quantities of the substance.[3] It took until 1971 until a practical synthesis was published. The synthesis starts by combining hydrazine and diethyl carbonate. The product of this step is reacted with phenyl isocyanate to form 4-Phenyl-1-carbethoxysemicarbazide (4), which is cyclized with base to form 4-Phenylurazole (5). Oxidation with tert-Butyl hypochlorite then yields PTAD (6).[4]