Alcohols Oppenauer oxidation

Ophirin B, via ring-closing diene metathesis, 11, 236 Ophthamology, silicone applications, 3, 680 Oppenauer oxidation, alcohols, 3, 278-279 Optical properties... 

Secondary alcohols may be oxidised to the corresponding ketones with aluminium ferf.-butoxlde (or tsopropoxlde) In the presence of a large excess of acetone. This reaction Is known as the Oppenauer oxidation and Is the reverse of the Meerweln - Ponndorf - Verley reduction (previous Section) it may bo expressed ... 

The widely used Moifatt-Pfltzner oxidation works with in situ formed adducts of dimethyl sulfoxide with dehydrating agents, e.g. DCC, AcjO, SO], P4O10, CCXTl] (K.E, Pfitzner, 1965 A.H. Fenselau, 1966 K.T. Joseph, 1967 J.G. Moffatt, 1971 D. Martin, 1971) or oxalyl dichloride (Swem oxidation M. Nakatsuka, 1990). A classical procedure is the Oppenauer oxidation with ketones and aluminum alkoxide catalysts (C. Djerassi, 1951 H. Lehmann, 1975). All of these reagents also oxidize secondary alcohols to ketones but do not attack C = C double bonds or activated C —H bonds. 

The oxidation of a hydroxyl group by an aluminum alkoxide-catalyzed hydrogen exchange with a receptor carbonyl compound is known as the Oppenauer oxidation. For oxidation of steroidal alcohols the reaction is generally... 

Oppenauer oxidation, 236 Oxidation of allylic alcohols with dichloro-dicyanobenzoquinone, 248 Oxidation of allylic alcohols with manganese dioxide, 247... 

The reduction of ketones to secondary alcohols and of aldehydes to primary alcohols using aluminum alkoxides is called the Meerw>ein-Ponndorf-Verley reduction. The reverse reaction also is of synthetic value, and is called the Oppenauer oxidation. ... 

The reverse reaction, the so-called Oppenauer oxidation, is carried out by treating a substrate alcohol with aluminum tri-r-butoxide in the presence of acetone. By using an excess of acetone, the equilibrium can be shifted to the right, yielding the ketone 1 and isopropanol ... 

Isopropyl Alcohol and Aluminum Isopropoxide. This is called the Meer-wein-Ponndotf-Verley reduction It is reversible, and the reverse reaction is known as the Oppenauer oxidation (see 19-3) ... 

The Oppenauer Oxidation. When a ketone in the presence of base is used as the oxidizing agent (it is reduced to a secondary alcohol), the reaction is known as the Oppenauer oxidation. This is the reverse of the Meerwein-Ponndorf-Verley reaction (16-23), and the mechanism is also the reverse. The ketones most commonly used are acetone, butanone, and cyclohexanone. The most common base is aluminum r r/-butoxide. The chief advantage of the method is its high selectivity. Although the method is most often used for the... 

The Oppenauer oxidation makes use of ketones (typically acetone) or alkenes as hydrogen acceptors and this absence of a strong oxidising agent allows to overcome some potential NHC oxidative instability. Reactions consist of an equilibrium between an alcohol and its oxidised form (Scheme 10.9). 

There are also reactions in which hydride is transferred from carbon. The carbon-hydrogen bond has little intrinsic tendency to act as a hydride donor, so especially favorable circumstances are required to promote this reactivity. Frequently these reactions proceed through a cyclic TS in which a new C—H bond is formed simultaneously with the C-H cleavage. Hydride transfer is facilitated by high electron density at the carbon atom. Aluminum alkoxides catalyze transfer of hydride from an alcohol to a ketone. This is generally an equilibrium process and the reaction can be driven to completion if the ketone is removed from the system, by, e.g., distillation, in a process known as the Meerwein-Pondorff-Verley reduction,189 The reverse reaction in which the ketone is used in excess is called the Oppenauer oxidation. 

Hydrogen transfer reactions from an alcohol to a ketone (typically acetone) to produce a carbonyl compound (the so-caUed Oppenauer-type oxidation ) can be performed under mild and low-toxicity conditions, and with high selectivity when compared to conventional methods for oxidation using chromium and manganese reagents. While the traditional Oppenauer oxidation using aluminum alkoxide is accompanied by various side reactions, several transition-metal-catalyzed Oppenauer-type oxidations have been reported recently [27-29]. However, most of these are limited to the oxidation of secondary alcohols to ketones. 

The reversible reduction of aldehydes or ketones to the corresponding alcohols using aluminum alkoxides such as aluminum isopropoxide (Al[OCH(CH3)2]3), the reducing alcohol usually being isopropyl alcohol (Le., RCOR + CH3CH(0H)CH3 RCH(OH)R + CH3C0CH3). The reaction is facilitated by the removal of acetone by distillation". This reaction has served as a model for metal-ion-dependent hydride transfer reactions catalyzed by certain enzymes. The reverse reaction is known as the Oppenauer oxidation . ... 

Catalytic reduction of codeine gives dihydrocodeine and Oppenauer oxidation (a ketone such as acetone and an aluminum alkoxide, the ketone being reduced to an alcohol) gives hydrocodone. Hydrocodone can also be prepared directly from codeine with a metal catalyst, which isomerizes the allylic alcohol to a ketone. Codeine is prepared by methylation of morphine, which is isolated from the opium poppy. Hydrocodone is more potent than codeine. Acetaminophen is a mild analgesic and is discussed in Section 8. 

Meerwein-Pondorf-Verley reduction, discovered in the 1920s, is the transfer hydrogenation of carbonyl compounds by alcohols, catalyzed by basic metal compounds (e.g., alkoxides) [56-58]. The same reaction viewed as oxidation of alcohols [59] is called Oppenauer oxidation. Suitable catalysts include homogeneous as well as heterogeneous systems, containing a wide variety of metals like Li, Mg, Ca, Al, Ti, 2r and lanthanides. The subject has been reviewed recently [22]. In this review we will concentrate on homogeneous catalysis by aluminium. Most aluminium alkoxides will catalyze MPV reduction. 

In steroidal alcohols the 3a- or 3P-hydroxy group (18, Table 10) is selectively oxidized in the presence of the 17P-hydroxy group. The yield obtained corresponds to that of the Oppenauer-oxidation which is the most selective oxidation method for the 3-OH group. 

The reverse reaction is known as the Oppenauer oxidation. Here aluminium tri tertiary but oxide and an involatile ketone such as cyclohexanone are used to oxidise any secondary alcohol to the corresponding ketone. 

Pyrrolizidine alcohols are readily oxidized. Stereoisomeric 1-hydroxymethylpyrrolizidines when oxidized with chromic acid afford stereoisomeric pyrrolizidine-1-carboxylic acids (see Section III, C).81,90 Secondary alcohols, when subjected to Oppenauer oxidation or chromic acid treatment, yield amino-ketones (cf. refs. 72, 77, and 81). 

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