Copper/Persulfate‐Promoted Oxidative Decarboxylative C−H Acylation of Pyrazolones with α‐Oxocarboxylic Acids: Direct Access to 4‐Acylpyrazolones under Mild Conditions.

Abstract: A facile and efficient oxidative C−H acylation of N‐substituted pyrazolones using α‐oxocarboxylic acids as an acyl group source was developed. A combination of Cu(OAc)2 and K2S2O8 enables the reaction to proceed smoothly under air and provides a wide array of 4‐acylpyrazolone products in moderate to excellent yields. The mechanism of this transformation is believed to proceed via a copper‐induced decarboxylation to form the acyl‐copper species. This method provides a convenient and useful route for a direct installation of an acyl moiety into bioactive pyrazolone derivatives, which can be further utilized in many applications. [ABSTRACT FROM AUTHOR]