Oxidation of ketone by palladium(II). a-Hydroxyketone synthesis catalyzed by a bimetallic palladium(II) complex Arab K. El-Qisairi *, Hanan A. Qaseer Department of Chemistry, Mu’tah University, PO Box 37, Mu’tah, Jordan Received 14 March 2002; accepted 20 May 2002 Abstract A bimetallic palladium(II) complex containing a triketone ligand and a bridging dinitrogen ligand oxidizes ketones in aqueous THF to a-hydroxyketone by a direct air oxidation. While the normal synthesis of a-hydroxyketones involves a series of reactions, this synthesis performs the transformation in one step in a catalytic air oxidation. This synthesis does not involve an olefin and is almost unprecedented in transition metal catalysis. Its main virtue is its simplicity and actually it is an enolization reaction. Methanesulfonic acid is used to accelerate the enolization of ketones. The reaction is carried out in the presence of CuCl 2 and/or dioxygen only. In particular, it is found that the hydroxyketone formation does not require the presence of CuCl 2 . Matrix assisted laser desorption ionization (MALDI) and time-of-flight mass spectrometry (TOFMS) are used to record the mass spectra of a- hydroxyketones products. a-Cyano-4-hydroxycinnamic acid (CHCA) matrix promoted the molecular ion detection when 180 pmol of a-hydroxyketones is introduced into the TOFMS. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Palladium(II); Catalysis; Hydroxyketone 1. Introduction The oxidation of carbonyl compounds by metal species is a well-known and widely studied reaction [1  /3]. Many of these apparently proceed by oxidation of the enol tautomer. Thus, the oxidation of ketones by the two-electron oxidants, Hg(II), Tl(III) and Mn(VII), were postulated to involve the enol isomer [4]. Some one-electron oxidants such as Mn(III) [5] and tris(1,10- phenanthroline) complexes of Fe(III) and Ru(III) [6] also attack the enol isomer. Recently, palladium(II) chloride has been used in the catalytic carbonylation of ketones [7]. A number of important compounds that show inter- esting pharmacological properties possess a-hydroxy- carbonyl groupings, which are common structural features of many natural products. Furthermore, a- hydroxycarbonyl groupings are useful chiral building units in the preparation of biologically active com- pounds. The isomerization of a-hydroxycarbonyl com- pounds is of crucial importance in metabolism [8]. The importance of a-hydroxyketones mentioned above brought us to investigate and describe the catalytic oxidation of ketones using achiral bimetallic catalyst A, while the asymmetric version reactions are now under processing [9]. * Corresponding author. Tel.:  /962-6-461-7890x4610; fax:  /962-6- 465-4061 E-mail addresses: aqaseer@mutah.edu.jo, aqaseer@yahoo.com (H.A. Qaseer). Journal of Organometallic Chemistry 659 (2002) 50  /55 www.elsevier.com/locate/jorganchem 0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0022-328X(02)01691-1