Ketones unsaturated, hydrogenation

Reduction of a,P-unsaturated ketones Hydrogenation of olefin conjugated with carbonyl group... 

Chlorosulfonic acid Saturated and unsaturated acids, acid anhydrides, nitriles, acrolein, alcohols, ammonia, esters, HCl, HF, ketones, hydrogen peroxide, metal powders, nitric acid, organic materials, water... 

When the a,P-unsaturated ketone is hydrogenated to the alcohol, a product with an intense sandalwood odor is produced (162). Many other examples of useful products have been made by condensation of campholenic aldehyde with ketones such as cyclopentanone and cyclohexanone. 

Intramolecular hydrogen-atom abstraction is also an important process for acyclic a,/ -unsaturated ketones. The intermediate diradical then cyclizes to give the enol of a cyclobutyl ketone. Among the by-products of such photolyses are cyclobutanols resulting from alternative modes of cyclization of the diradical intermediate ... 

The dienol is unstable, and two separate processes have been identified for ketonization. These are a 1,5-sigmatropic shift of hydrogen leading back to the enone and a base-catalyzed proton transfer which leads to the / ,y-enone. The deconjugated enone is formed because of the kinetic preference for reprotonation of the dienolate at the a carbon. Photochemical deconjugation is a synthetically useful way of effecting isomerization of a,) -unsaturated ketones and esters to the j ,y-isomers. 

As is clear from the preceding examples, there are a variety of overall reactions that can be initiated by photolysis of ketones. The course of photochemical reactions of ketones is veiy dependent on the structure of the reactant. Despite the variety of overall processes that can be observed, the number of individual steps involved is limited. For ketones, the most important are inter- and intramolecular hydrogen abstraction, cleavage a to the carbonyl group, and substituent migration to the -carbon atom of a,/S-unsaturated ketones. Reexamination of the mechanisms illustrated in this section will reveal that most of the reactions of carbonyl compounds that have been described involve combinations of these fundamental processes. The final products usually result from rebonding of reactive intermediates generated by these steps. 

The product stereochemistry obtained on hydrogenation of a, -unsaturated ketones is generally the same as that observed on saturation of the corresponding desoxy olefin. However, the stereochemistry of hydrogenation of these polarized species can be affected by the nature of the solvent (see section II-C). 

Epoxidation of a, -Unsaturated Ketones with Alkaline Hydrogen Peroxide ... 

It is possible to monitor the reaction and determine the end point by the absence of an a,/S-unsaturated ketone absorption in the UV or by the determination of the consumption of ca. one molar equivalent of hydrogen peroxide by permanganate titration. 

Photoketone (118) has served as the key intermediate in a relatively simple transformation of 3-keto-10/ -steroids to 3-keto-lOa-isomers without the assistance of other functional groups suitably situated next to the ring junction—a task that appears difficult to attempt by other methods. Optimal yields of (118) are achieved by catalytic hydrogenation of the unsaturated ketone (175), the photoisomer of 1-dehydrotestosterone acetate (see section III-C). In this way, a 6-step conversion of 1-dehydrotestosterone acetate (174) to IOa-testosterone acetate (127 acetate) is achieved in good yield. ° ... 

As in the case of the steroids, introduction of additional nuclear substituents yields morphine analogs of increased potency. The more important of these are derived from one of the minor alkaloids that occur in opium. Thebaine (14), present in crude opium in about one-tenth the amount of morphine, exhibits a reactive internal diene system that is well known to undergo various addition reactions in a 1,4 manner (e.g., bromination). Thus, reaction with hydrogen peroxide in acid may be visualized to afford first the 14-hydroxy-6-hemiketal (15). Hydrolysis yields the isolated unsaturated ketone (16). Catalytic reduction... 

Reduction of unsaturated aldehydes seems more influenced by the catalyst than is that of unsaturated ketones, probably because of the less hindered nature of the aldehydic function. A variety of special catalysts, such as unsupported (96), or supported (SJ) platinum-iron-zinc, plalinum-nickel-iron (47), platinum-cobalt (90), nickel-cobalt-iron (42-44), osmium (<55), rhenium heptoxide (74), or iridium-on-carbon (49), have been developed for selective hydrogenation of the carbonyl group in unsaturated aldehydes. None of these catalysts appears to reduce an a,/3-unsaturated ketonic carbonyl selectively. 

Compound A, C H O, was found to be an optically active alcohol. Despite its apparent unsaturation, no hydrogen was absorbed on catalytic reduction over a palladium catalyst. On treatment of A with dilute sulfuric acid, dehydration occurred and an optically inactive alkene B, Q iH14, was produced as the major product. Alkene B, on ozonolysis, gave two products. One product was identified as propanal, CH3CH2CHO. Compound C, the other product, was shown to be a ketone, CgHgO. How many degrees of unsaturation does A have Write the reactions, and identify A, B, and C. 

Treatment of an or.jS-unsaturated ketone with basic aqueous hydrogen peroxide yields an epoxy ketone. The reaction is specific to unsatnrated ketones isolated alkene double bonds do not react. Propose a mechanism. 

In a, 3-unsaturated ketones, nitriles, and esters (e.g., 125), the y hydrogen assumes the acidity normally held by the position a to the carbonyl group, especially when R is not hydrogen and so cannot compete. This principle, called vinylology, operates because the resonance effect is transmitted through the double bond. However, because of the resonance, alkylation at the a position (with allylic rearrangement) competes with alkylation at the y position and usually predominates. 

Ion 21 can either lose a proton or combine with chloride ion. If it loses a proton, the product is an unsaturated ketone the mechanism is similar to the tetrahedral mechanism of Chapter 10, but with the charges reversed. If it combines with chloride, the product is a 3-halo ketone, which can be isolated, so that the result is addition to the double bond (see 15-45). On the other hand, the p-halo ketone may, under the conditions of the reaction, lose HCl to give the unsaturated ketone, this time by an addition-elimination mechanism. In the case of unsymmetrical alkenes, the attacking ion prefers the position at which there are more hydrogens, following Markovnikov s rule (p. 984). Anhydrides and carboxylic acids (the latter with a proton acid such as anhydrous HF, H2SO4, or polyphosphoric acid as a catalyst) are sometimes used instead of acyl halides. With some substrates and catalysts double-bond migrations are occasionally encountered so that, for example, when 1 -methylcyclohexene was acylated with acetic anhydride and zinc chloride, the major product was 6-acetyl-1-methylcyclohexene. ... 

Asymmetric syntheses of warfarin <96TL8321> and the axially chiral bicoumarin, isokotanin A <96TL3015> have been reported. The former is based on a Rh-catalysed asymmetric hydrogenation of a 3-(a,P-unsaturated ketone) substituted coumarin, whilst the key steps of the latter are an asymmetric Ullmann coupling and a selective demethylation. The stereochemistry of the fused dihydrocoumarin resulting from Li/NHs reduction of... 

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