Fetizons Oxidation

The available experimental data4 are consistent with the following mechanism for the oxidation of alcohols with silver carbonate on Celite  

The initial chemisorption step can be prevented by many ligands including quite weak ones. Thus, Fetizon s oxidation must be performed in very apolar solvents because even solvents with very weak basicity, such as ethyl acetate or methyl ethyl ketone, severely inhibit the oxidation.40 That is why, Fetizon s oxidation is routinely performed in boiling benzene, which is 

Interestingly, when solvents possessing a lower polarity than benzene—such as heptane—are employed, a substantial acceleration of the oxidation can be observed. Thus, endo-2-norbornanol (70) is oxidized 11 times faster in heptane than in benzene.5 In fact, even weak ligands such as alkenes can produce a substantial slowing of the oxidation. For example, endo-2-norbornenol (71) reacts 50 times slower than endo-2-norbornanol (70) with Fetizon s reagent.5 

Unsurprisingly, examples from successful oxidations of alcohols possessing other polar functionalities with Fetizon s reagent are quite absent from the literature. 

Optimum oxidation conditions involve a maximum of silver carbonate surface available for chemisorption. That is why, increasing the amount of Celite on which silver carbonate is precipitated produces a higher rate of oxidation. Although, above a value of 900 g of Celite per mol of silver carbonate, a slight decrease of oxidation speed is observed resulting from a dilution effect.40 

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A.g2C03 ( Fetizon Oxidation) also Ag2C03/celite... 

Ag2C03 (Fetizon Oxidation) also Ag2COs/celite Synthesis 1979, 401... 

Other references related to the Fetizon oxidation are cited in the literature. " ... 

The products are ds-fused. They are hydrolyzed by TsOH in aqueous THF to lactols, which can be oxidized by Fetizon s reagent to lactones or converted to dials by DBU. The enol ether group of the adduct can be selectively oxidized by Cl-QH4CO3H or OsO to provide bicyclic tetrahydrofurans. 

Swern s reagent. It is oxidized to 4 by Fetizon s reagent in quantitative yield and by barium manganatc in 92% overall yield. 

Silver carbonate on Celite has been the preferred reagent for this oxidation (3, 247), but 10-20 equivalents of oxidant is required. In addition the regioselectivity is highly dependent on the solvent. Thus 2 is oxidized by Fetizon s reagent in CH2C12/C6H6 to a 1 1 mixture of 3 and 4-ketopentanol-l (4), but in CHC13 to 3 and 4 in the ratio 9 1. 

Because of the mildness of Fetizon s reagent and its sensitivity to minor structural features, this oxidant is particularly well-suited for the mono oxidation of symmetric diols7 and for the oxidation of 1,2-diols in which one of the alcohols is tertiary.8... 

General Procedure for Oxidation of Alcohols with Fetizon s Reagent... 

An alcohol is oxidized with Fetizon s reagent in the presence of a very oxidation-sensitive dialkoxy alkene that, for instance, suffers selective cleavage with no reaction on the alcohol moiety on contact with PCC. 

The oxidation of this alcohol can be carried out employing Fetizon s reagent under simple experimental conditions with quantitative yield. Alternatively, a Swem oxidation can be used resulting in 92% yield. 

Functional Group and Protecting Group Sensitivity to Fetizon s Oxidation... 

As Fetizon s oxidation is carried out under neutral conditions, acid-and base-sensitive protecting groups resist its action. The oxidation-sensitive p-methoxybenzyl (PMB) protecting group resists the action of Fetizon s reagent.12... 

Fetizon s reagent has a great tendency to oxidize lactols to lactones, relative to the oxidation of primary and secondary alcohols.40 Therefore, this reagent is very often able to transform lactols into lactones in the presence of unreacting alcohols.15... 

A corollary of this selectivity is the very easy transformation of diols into lactones with silver carbonate on Celite .16 During the oxidation of a diol with Fetizon s reagent, as soon as an intermediate hydroxyaldehyde is able to equilibrate with a certain proportion of hemiacetal—even if present... 

The treatment of 1,6-hexanediol with Fetizon s reagent leads to an intermediate hydro-xyaldehyde that equilibrates with a small amount of hemiacetal, which is further oxidized to... 

Although amines can react with Fetizon s reagent resulting in the formation of enamines19 or imminium cations that can be trapped in situ,20 it is very often possible to oxidize alcohols without affecting tertiary amines in the same molecule.21... 

Among common alcohol oxidants, Fetizon s reagent—due to its mildness—is particularly well-suited for the selective oxidation of secondary alcohols (see page 283). 

Fetizon s reagent is able to oxidize an unhindered secondary alcohol in the presence of a primary one in an 80% yield. 

On the other hand, Fetizon s reagent is very sensitive to steric hindrance and no selective oxidation of secondary alcohols is possible in many complex substrates.4... 

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