1.3- Diphenyl-5-imino-2-pyrazoline

The decarboxylation of l,3-diphenyl-5-imino-2-pyrazolin-3-carboxylic acid gives l,3-diphenyl-5-imino-2-pyrazoline.506 Druey and Schmidt391 have taken advantage of the selective replacement of an oxo group by chlorine over that of an imino group to prepare 5-imino-2-pyrazolines (eq. 95). 

Synthetic methods involving conversion of other, but similar, ring systems to 3,5-pyrazolidinediones have been reduction of 1,2-diphenyl-3,4,5-pyrazolidinetrione with tin and hydrochloric acid63 and hydrolysis of 5-imino-3-pyrazolidinones (3-amino-2-pyrazolin-5-ones) with acid.1339,1596... 

---