A Copper-, Phosphorous- and Solvent-free Coupling of Acyl Halides with Terminal Alkynes Catalyzed by Palladium-Cryptand-22 Complex under Aerobic Conditions

Ynones or α,β-acetylenic ketones are useful synthetic intermediates for the preparation of many biologically-active compounds and heterocyclic derivatives such as pyrroles, furanes, furanones, pyrazoles, and isoxazoles.¹ Different methodologies for the preparation of α,β-acetylenic ketones have been reported in which various metals have been employed as catalysts.² Unfortunately, there are several disadvantages that confine the utility of the given protocols. Namely, copper salts which are very much likely to form diynes have been used as a co-catalyst in many studies. Moreover, phosphorous containing ligands have made the reaction conditions harsher owing to the need of inert atmosphere such as argon and nitrogen. The use of hazardous organic solvents and high temperatures are also unfavorable. In this study, we have successfully demonstrated a solvent-, copper- and phosphorous-free cross-coupling reaction of terminal alkynes with acyl halides catalyzed by Pd-Cryptand-22 as catalyst. This catalyst was simply prepared and showed air and moisture stability. The reaction was performed at room temperature and under aerial conditions using triethylamine as base. The simple, mild and green procedure, short reaction times and moderate to excellent yields make this method well-suited for ynone synthesis. References: [1] (a) Zora, M.; Kivrak, A.; Yazici, C. J. Org. Chem. 2011, 76, 6726; (b) Karpov, A. S.;Merkul, E.; Oeser, T.;Muller, T. J. J. Eur. J. Org. Chem. 2006, 13, 2991. [2] Perrone, S.; Bona, F.; Troisi, L. Tetrahedron 2011, 67, 738.