Organophosphane-Catalyzed Direct β-Acylation of 4-Arylidene Pyrazolones and 5-Arylidene Thiazolones with Acyl Chlorides.

An efficient method for the direct β-acylation of arylidene pyrazolones and thiazolones with acyl chlorides in the presence of a base catalyzed by organophosphanes is reported. A variety of functionalized 4-arylidene pyrazolone and 5-arylidene thiazolone derivatives were prepared under metal-free and mild conditions via a tandem phospha-Michael addition/O-acylation/intramolecular cyclization/rearrangement sequence. Our mechanistic investigations revealed that the reaction is highly stereospecific to provide exclusively cis-isomers, and the methodology can also be scaled up with similar efficacy.