Reactions with 3-Pyrazolin-5-ones: Synthesis of some 4-Substituted 2,3-Dimethyl-1-phenyl-3-pyrazolin-5-ones

4-Acetylantipyrine (1) was condensed with aromatic or heterocyclic aldehydes to yield the cinnamoylidene derivatives 4a—d. Compound 4b was converted into the pyrazolinylantipyrine derivative 9 by hydrazine hydrate. 4-(Chloroacetyl)antipyrine (2) reacted with aldehydes to yield the furan-2-one derivatives 11 or the dihydroxy derivative 12. The behaviour of 4-formylantipyrine toward methylenenitriles was investigated.