Ethyl ketones, oxidative cleavage

The oxidative cleavage of unsaturated ketones takes place under the same conditions as that of alkenes or other unsaturated derivatives. The fate of the primary fission product depends on the position of the double bond with respect to the carbonyl group and on the subsequent reactions. Ozonization of A -cholestenone in acetic acid and ethyl acetate, followed by treatment with 30% hydrogen peroxide, gives a keto acid, evidently resulting from the decomposition of the primarily formed diketo acid (equation 444) [1176]. 

Table II shows results for the electro-oxidation of secondary alcohols and ketones. In alkaline electrolyte, secondary butanol was not oxidized to methyl ethyl ketone but was cleaved to acetate. Similarly methyl ethyl ketone was cleaved to acetate, although some CO2 and propionate formed, indicative of cleavage on the other side of the carbonyl group. Butanediol (2 ) went to acetate yielding less CO2. At pH 9 in borax buffer 2 Trtanol went exclusively to methyl ethyl ketone at 89% conversion, suggesting that enolization in alkali is a necessary part of the cleavage process. Cyclohexanol and cyclohexanone were both converted to adipic acid. Figure 12 summarizes the various types of electro-organic oxidations, thus far discussed, which are observed to occur on lead ruthenate in alkaline electrolyte.

The preparation of the methyl ketone required for the aldol coupling reaction was accomplished by using the asymmetric alkylation of the unsaturated amide 158 according to a protocol developed by Myers [112]. Asymmetric alkylation of 158 with ethyl iodide gave 159 which was reduced to the primary alcohol (LiNH2, BH3) and protected as a PMB ether to produce, after oxidative cleavage of the olefin, the methyl ketone 160 which was converted to the trimethylsilyl enol ether 161 (LiHMDS, TMSC1) (Scheme 31). 

Another prominent example of a chiral auxiliary for highly diastereoselective synthesis of iyn-aldol adducts was developed by Masamune utilizing (/ )-mandelic acid (Scheme 2.111) [12]. This early example of chiral ethyl ketone takes advantage of the mandelic acid as the chiral source and liberation of the corresponding acid though oxidative cleavage. 

Tertiary alcohols are oxidized in water-dioxane-NaOH to alkoxy radicals, wliich fragmentate to ketone and alkyl radicals R- (Eq. (216) ). The relative rate of cleavage decreases with R in the order sec -butyl > isopropyl > ethyl > propyl > pentyl > isobutyl > methyl 46 8). Likewise, the bisulfite adduct of cyclohexanone is converted in 20% yield to 4-hydroxyhexanoic acid lactone (160) and 3-hydroxycyclohexanoic acid lactone (161) by anodic fragmentation (Eq. (222) ) 469 ... 

A large proportion of the volatiles identified in vegetable oils are derived from the cleavage reactions of the hydroperoxides of oleate, linoleate, and linolenate (Section D). A wide range of hydrocarbons (ethane, propane, pentane and hexane) appears to be formed in soybean oil oxidized to low peroxide values. A number of volatiles identified in vegetable oils that are not expected as primary cleavage products of monohydroperoxides include dialdehydes, ketones, ethyl esters, nonane, decane, undecane, 2-pentylfuran, lactone, benzene, benzaldehyde and acetophenone. Some of these volatiles may be derived from secondary oxidation products, but the origin of many volatiles still remains obscure. However, studies of volatile decomposition products should be interpreted with caution, because the conditions used for isolation and identification may cause artifacts, especially when fats are subjected to elevated temperatures. 

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