Aerobic oxidation of secondary alcohols

He J, Wu T, Jiang T et al (2008) Aerobic oxidation of secondary alcohols to ketones catalyzed by cobalt(II)/ZnO in poly(ethylene glycol)/C02 system. Catal Commun 9(13) 2239-2243... 

Chiral N-arylated imidazolinylidene ligands have been employed in the palladium(II) catalyzed aerobic oxidation of secondary alcohols to the corresponding ketones [55]. The chiral variant of this reaction, which does not generate a new element of chirality, is again based on the kinetic resolution of racemic mixtures. The active catalyst is formed in situ by a combination of two precursors, a dinuclear NHC-palladium(II) complex and an achiral (acetate) or chiral base ((-)-sparteine) (Scheme 18). 

A number of systems consist of a palladium salt, typically PdCb or Pd(OAc)2, with abase. For example, PdCb-NaOAc catalyzes the aerobic oxidation of secondary alcohols in ethylene carbonate under nuld conditions. Sheldon has carried out mechanistic investigations on a number of related Pd systems and shown that water-soluble complexes of Pd(II) with phenanthrohnes are stable, recyclable catalysts for the selective aerobic oxidation of a wide range of alcohols to aldehydes, ketones, and carboxylic acids in a biphasic liquid liquid system. The active catalyst is a dihydroxy-bridged palladium dimer. 

CuC1-DEADH2]-Catalyzed Aerobic Oxidation of Secondary Alcohols with 2 Equivalents K2C03 90)... 

Krishnan S, Bagdanoff JT, Ebner DC, Ramtohul YK, Tambar UK, Stoltz BM (2008) Pd-Catalyzed Enantioselective Aerobic Oxidation of Secondary Alcohols Applications to the Total Synthesis of Alkaloids. J Am Chem Soc. 130 13745... 

Table 5.2 Ruthenium/quinone/Co-salen-catalyzed aerobic oxidation of secondary alcohols. ...

Ruthenium compounds are widely used as catalysts in organic synthesis and have been extensively studied as catalysts for the aerobic oxidation of alcohols In 1978, Mares and coworkers reported that RuCls.nHjO catalyzes the aerobic oxidation of secondary alcohols into the corresponding ketones, albeit in modest yields. Subsequently, RUCI3 and RuCl2(Ph3P)j were shown to catalyze the aerobic oxidation of activated allylic and benzylic alcohols under mild conditions, e.g. the oxidation of retinol to retinal (Reaction 2). 

Chromium(VI) catalyzes the oxidation of alcohols with alkyl hydroperoxides . Chromium-incorporated molecular sieves, in particular chromium-substituted aluminophosphate-5 (Cr-APO-5) were shown to be effective for the aerobic oxidation of secondary alcohols to the corresponding ketones (Reaction 19). This, and related catalysts, were first believed to be heterogeneous but more detailed investigations revealed that the observed catalysis is due to small amounts of soluble chromium that are leached from the framework by reaction with hydroperoxides. Reaction 19 may involve initial chromium-catalyzed free radical autoxidation of the alcohol to the a-hydroxyalkyl hydroperoxide followed by chromium-catalyzed oxygen transfer with the latter and/or H202 (formed by its dissociation) via an oxochromium(VI)-chromium(IV) cycle. 

Type of reaction C-O bond formation Reaction conditions Acetonitrile, room temperature Synthetic strategy Aerobic oxidation of secondary alcohols Catalyst A -Hydroxyphthalimide (NHPI)/Fe(N03)3.9H20... 

Zhao, H., Sun, W., Miao, C., and Zhao, Q. (2014). Aerobic oxidation of secondary alcohols using NHPI and iron salt as catalyst at room temperature. J. Mol. Catal. A Chem., 393, 62-67. 

Caspi, D., Ebner, D., Bagdanoff, J., et al. (2004). The Resolution of Important Pharmaceutical Building Blocks by Palladium-Catalyzed Aerobic Oxidation of Secondary Alcohols, A fv. Syrah. Catal., 346, pp. 185-189. 

Fig. 24 Aerobic oxidation of secondary alcohols with bifunctional amido Ir catalyst...

The temperature used in the oxidation of the diols 3,35°C, is probably the lowest temperature reported for a hydrogen transfer reaction with the Shvo catalyst The aerobic oxidation of secondary alcohols using Shvo s catalyst 1 was recently combined with an efficient hybrid electron transfer mediator 5 (6) [47, 48], This leads to a facile aerobic oxidation via transfer dehydrogenation, whereas the previous system (cf. electron transfer system of Scheme 3) [41, 42] with separate quinone and metal macrocycle now has been modified by tethering the quinone to the metal macrocycle (Scheme 3). 

In contrast to the Cu/TEMPO combination, Fe(III)/TEMPO systems readily catalyze the aerobic oxidation of secondary alcohols and do not usually require any base or less stericaUy hindered ligands. The best activity was observed with weakly coordinating solvents (e.g., dichloroethane) unlike Cu/TEMPO systems, which normally are more active in acetonitrile. The performance and substrate scope (primary and secondary aUyHc, benzylic, or inactivated aliphatic alcohols) of Fe—TEMPO catalyst systems is improved by the presence of NaCl. ... 

Caspi DD, Ebner DC, Bagdanoff JT, Stoltz BM. The resolution of important pharmaceutical building blocks by palladium-catalyzed aerobic oxidation of secondary alcohols. Adv. Synth. Catal. 2004 346 185-189. 

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