Tanakorn Kittikool, Tarm Viriyanukul, Kunita Phakdeeyothin, and Sirilata Yotphan*
         Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, 10400 Bangkok, Thailand E-mail: sirilata.yot@mahidol.ac.th
            Pyrazolones are nitrogen-containing heterocyclic precursors that have been extensively studied over the years due to their prevalence as core structures in biologically and pharmacologically relevant molecules. They are also versatile in organic synthesis, coordination chemistry, and agrochemistry applications. Throughout the past decade, various pyrazolone derivatives are being utilized for several biological screening including antimicrobial, antiviral, anticancer, antitumor, antioxidant,antidiabetic, and anti inflammatory activities. In this work, we have developed a simple and efficient Pd-catalyzed-site-selective direct acetoxylation of pyrazolones using PIDA as both an acetoxy source and the oxidant. A wide variety of 4-acetoxylated pyrazolones products were synthesized with complete site-selectivity under mild reaction conditions. Unexpectedly, in the absence of Pd catalyst, we found that a methyl acetate product was formed instead under metal-free conditions. These switchable-regioselective acetoxylation approaches offer the effective and straightforward strategy for pyrazolone functionalization; thus, providing great potential for further modification of synthetic molecules.