Catalysis of Organic..

Tanielyan et al. 11915. Transition Metal FreeCatalytic Aerobic Oxidation of AlcoholsUnder Mild ConditionsUsing Stable Nitroxyl Free RadicalsSetrak K. Tanielyan 1 , Robert L. Augustine 1 , Clementina Reyes 1 , NagendranathMahata 1 , Michael Korell 2 , Oliver Meyer 31 Center for Applied Catalysis, Seton Hall University, South Orange, NJ 070792 Degussa Corp., BU Building Blocks, Parsippany, NJ 070543 Degussa AG, BU Building Blocks, Marl 45764, GermanyAbstracttanielse@shu.eduThe oxidation of alcohols to the corresponding aldehydes, ketones or acidsrepresents one of the most important functional group transformations in organicsynthesis. While this is an established reaction, it still presents an importantchallenge (1). Although there are numerous oxidation methods reported in theliterature, only a few describe the selective oxidation of primary or secondaryalcohols to the corresponding aldehydes or ketones utilizing TEMPO based catalystsystems in combination with clean oxidants such as O 2 and H 2 O 2 (2). The mostefficient, common, TEMPO based systems require the use of substantial amounts ofexpensive and/or toxic transition metal complexes, which makes them unsuitable forindustrial scale production. Here, we report a highly effective aerobic oxidation ofprimary and secondary alcohols by a catalyst system, based on 4-acetamido-2,2,6,6-tetramethylpiperidin-1-oxyl (AA TEMPO), Mg(NO 3 ) 2 and N-bromosuccinimide(NBS) in an acetic acid solvent.IntroductionThe oxidation of alcohols to the corresponding aldehydes, ketones or acids certainlyrepresents one of the more important functional group transformations in organicsynthesis and there are numerous methods reported in the literature (1-3). However,relatively few methods describe the selective oxidation of primary or secondaryalcohols to the corresponding aldehydes and ketones and most of them traditionallyuse a stoichiometric terminal oxidant such as chromium oxide (4), dichromate (5),manganese oxide (6), and osmium or ruthenium oxides as primary oxidants (7).A convenient procedure for the oxidation of primary and secondary alcoholswas reported by Anelli and co-workers (8,9). The oxidation was carried out inCH 2 Cl 2 with an aqueous buffer at pH 8.5-9.5 utilizing 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 1) as the catalyst and KBr as a co-catalyst. The terminal oxidant inthis system was NaOCl. The major disadvantage of using sodium hypochlorite orany other hypohalite as a stoichiometric oxidant is that for each mole of alcoholoxidized during the reaction one mole of halogenated salt is formed. Furthermore,