An Atom-Efficient Catalytic Oxidation of Alcohols Using TEMPO/I 2 O 5 in Water
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An Atom-Efficient Catalytic Oxidation of Alcohols Using TEMPO/I2O5 in Water Zhong-Quan Liu Æ Xiaojie Shang Æ Lingzhi Chai Æ Qiuju Sheng
Received: 23 December 2007 / Accepted: 26 January 2008 / Published online: 13 February 2008 Ó Springer Science+Business Media, LLC 2008
Abstract A metal-free room-temperature oxidation of electron-rich alcohols to the corresponding aldehydes or ketones can be efficiently catalyzed by TEMPO/I2O5 in water. Keywords Oxidation Alcohols Aldehydes Ketones TEMPO Hypervalent Iodine
1 Introduction Oxidation of alcohols to the corresponding aldehydes or ketones is one of the most important functional group transformations in organic synthesis and numerous methods using a variety of reagents and conditions have been developed. Recent demand for greener, more atom efficient methods has encouraged the development of selective alcohol oxidation using safe, economic and environmentally benign agents [1]. In the area of metal-free catalytic alcohol oxidations relatively stable nitroxyl radicals (e.g., 2, 2, 6, 6-tetramethyl-piperidyl-1-oxyl, TEMPO) have emerged as the catalyst of choice [2–6]. However, the high cost and availability of TEMPO on large scale have encouraged the development of the variety of stoichiometric oxidants. Herein we wish to report an efficient selective catalytic oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones in water by using the most simple iodine (d)-based reagents: HIO3 (iodic acid, IA) and its anhydride I2O5 (iodine pentoxide, IP) as
the stoichiometric oxidants. Although the iodine (d) reagents such as 1-hydroxy-1,2-benziodoxal-3(1H)-one-1oxide (IBX) and Dess-Martin periodinane (DMP) have been successfully used for the oxidation of alcohols to the corresponding carbonyl compounds [7, 8, 9], most of these procedures were conducted in organic solvents such as DMSO, CH2Cl2 and acetone. Despite their extensive use in industry [10–12], IA and IP have rarely been employed in organic synthesis. According to the investigation of Nicolaou et al. [13], alcohols are inert to the unique simple iodine (d) reagents. Our research was inspired by the results of the TEMPO-Br2/I2 system by Miller et al. [14] and the PhIO-KBr system by Kita et al. [15]. Although these two systems are very efficient, both are suffered from overloading of the terminal oxidants and catalysts (Miller’s system: 2 eq. I2/10 mol% TEMPO/Toluene; Kita’s system: 2.2 eq. PhIO/ 10 mol% KBr or 1.1 eq. PhIO/ 1.0 eq. KBr). Combining with our former researches [16–18], we began to question that a TEMPO-catalyzed process with more atom-efficient stoichiometric IA and IP could be established. Fortunately, we successfully accomplished an efficient TEMPO-catalyzed alcohols oxidation at room temperature with a number of economic, commercially available, atom efficient, environmental friendly, and safe iodine (d) agents in water although it seems only electron-rich alcohols could be smoothly oxidized to the corresponding aldehydes and ketones (Scheme 1).
OH Z.-Q. Liu (&)
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