Über die Kondensation von Oxalsäureester mit Pyrazolonen

Abstract

P h e n y 1rn e t h yl-p y r a z o l o n (aus Acetessigester) kondensiert sich unter dem EinfluB von Keliumathylat rnit Oxalester zu dern 1 -P h e n y 1-3m e t h y 1 -5p y r a z 01 o n -4g 1 y ox y 1 sii u r e e s t e r (I).DaO es nicht die Methylgruppe ist, welche reagiert, sondern die Methengruppe in der 4-Stellung geht daraus hervor, daB das 1.3-Dip h e n y l -p y r a z o l o n (aus Benzoyl-essigeeter) in ganz gleicher Weis& den 1.3-D i p h e n y 1-5p y r a z o l o n -4 -g I y o x yl sa u r e e s t e r (11) liefert: N . c, E L N.CsHo N(' C0 I.

Synthesis of 3-Methyl-4-(4-methylbenzoyl)-1-phenyl-pyrazol-5-one: How To Avoid O-Acylation

“…Acylpyrazolones have been known since the end of the 19th century. The initial synthetic strategies have been based on classical Claisen condensation of esters with pyrazolone catalyzed by sodium salts of acids or sodium ethoxide, or on Fries rearrangement of O-acylated pyrazolones to C-acylated products by anhydrous zinc chloride (Scheme ) . However, both protocols have suffered with drawbacks such as low yields and colored side-products.…”