From Oppenauer oxidation

Commercially available aluminum isopropoxide, aluminum butoxide and aluminum phenoxide are generally of sufficient purity for use in Oppenauer oxidations provided that these reagents are obtained from a freshly opened container and are freely soluble in the reaction solvent. The reagents may be conveniently stored as 20-40 per cent solutions in anhydrous benzene or toluene. 

In the androstane and pregnane series the 7-methyl-A -3-ketones (36) are produced from 3j -acetoxy-A -7-ketones (34) with methyllithium, and subsequent Oppenauer oxidation of (35). ° ... 

Hydrolysis of the acetate (71) followed by Oppenauer oxidation gives B-norcholest-4-en-3-one in high yield. An analogous reaction sequence can be used to prepare B-norprogesterone and derivatives of B-nortestosterone from pregnenolone acetate and dehydroepiandrosterone acetate, respectively."" ... 

Oppenauer oxidation and spontaneous cychzation to give 73. This represents an interesting chemical route from the cinchona to the indole alkaloids. 

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. 

Yohimbine (36) is a well-known and reasonably available alkaloid from Corynanthe yohimbe, inter alia. For this reason, and partly because of its intrinsic pharmacological activity (including reputed aphrodisiac activity), chemists have frequently studied its properties. Oppenauer oxidation is usually attended by saponification and decarboxylation in this series, and yohimbone (37) is the product. Wolf-Kischner reduction to yohimbane (38), followed by sodium hydride mediated alkylation, leads to the analgesic agent, mimbane (39). °... 

The synthetic value of this reaction should be mentioned. Thus, current production of 5p-steroids from As-3(i-ols, readily available and cheap starting materials, requires a preliminary Oppenauer oxidation or fermentation to the A4-3-keto derivative followed by catalytic hydrogenation under alkaline conditions, as direct catalytic hydrogenation with both heterogeneous and homogeneous systems gives only the 5a isomer. 

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. 

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. 

Nuttalline was isolated from Lupinus nuttallii L. (155). The tetracyclic structure of nuttalline was established by dehydration of deoxonuttalline (112), obtained from nuttalline (113) by reduction with sodium borohydride, and by catalytic reduction to sparteine (6) (Scheme 20). Oppenauer oxidation of nuttalline gives 2,4-dioxosparteine (125). The UV spectrum of this 1,3-diketone... 

The selective oxidation of the 3P-hydroxy group in the presence of lip- and 20p-hydroxy groups in the triol 25 is unprecedented. In the Oppenauer-oxidation of similar compounds the 3P-OH group is oxidized in only 30% yield The remarkable selectivity obtained may be due to the fact that the 20p-hydroxy group is placed on the P-side of the steroid, remote from the electrode, which probably attacks from the less hindered a-side. 

It has been suggested that in Oppenauer oxidations using acetone, the genuine oxidant is one product, resulting from the autocondensation of acetone, possessing a higher oxidation potential.8... 

Not surprisingly, nowadays most Oppenauer oxidations are carried out employing cyclohexanone as oxidant because—for structural reasons— this ketone possesses an exceptionally high oxidation potential among ketones. Similarly, /V-methyI -4-pi peridone is used quite often because it possesses an oxidation potential close to cyclohexanone, while it is very easy to remove together with its reduction product from the reaction mixture by washing with aqueous acid.9... 

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