4-Phenyl-1,2,4-triazolin-3,5-dione: a powerful dienophile

✍ Scribed by R.C. Cookson; S.S.H. Gilani; I.D.R. Stevens

• Publisher: Elsevier Science
• Year: 1962
• Tongue: French
• Weight: 149 KB
• Volume: 3
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)70917-8

✦ Synopsis

DIENOPHILIC reactivity rises in the series fumaric acid, maleic acid, maleic anhydride' and the well recognized dienophilic properties of azodicarboxylic ester2 place it last in this series ahead of maleic anhydride. However, it fails to react (or reacts by allylic addition) with some dienes with which the latter reacts, a result which may be ascribed to the trans configuration of the nitrogen-nitrogen double bond. Constraining this bond into a & configuration ought, therefore, to enhance the dienophilic reactivity; a prediction borne out by a study of 4-phenyl-1,2,4-triazolin-3,5-dione (I).

The preparation of I (the N-phenylimide of azodicarboxylic acid) was reported as long ago as 1894 by Thiele3 and more recently by Stolle. 4 Both obtained it by oxidation of 4-phenylurazole; but the yields were rather low, probably due to the sensitivity of I to both acid and base.