Ketone into an ester

Baeyer-Villiger oxidation by trifluoraperoxyacetic acid converts a chlo-rofluoroalkyl ketone into an ester 7l ] (equation 63)... 

One of the most important methods for lactone preparation, and hence of the corresponding hydroxy acids (or halogeno acids, Section 5.14.1 above) is the Baeyer- Villiger rearrangment of cyclic ketones by the action of peracids. A wide variety of peracids have been used in this reaction but currently the reagents of choice are pertrifluoroacetic acid, m-chloroperbenzoic acid, and permaleic acid. The mechanism is formulated below for the conversion of an acyclic ketone into an ester. 

The conversion of an acyclic ketone into an ester or a cyclic ketone into a lactone is known as the Baeyer-Villiger reaction and can be accomplished chemically using a peradd (Scheme 4.18). Certain advantages can be... 

Yes, we have seen a way to do this also. Recall (from the previous chapter) that a Baeyer-ViUiger oxidation will convert a ketone into an ester ... 

RCO3H Baeyer-Villiger oxidation Converts a ketone into an ester (via insertion of an oxygen atom). Converts an aldehyde into a carboxylic acid (via insertion of an oxygen atom). 

The photorearrangement of a dienone was noted<4) as early as 1830 in a study of the sesquiterpene a-santonin (1). However, the structure and stereochemistry of the various photoproducts were not conclusively established until 1965.(6) Upon irradiation in neutral media, a-santonin (1) undergoes rapid rearrangement to the cyclopropyl ketone, lumisantonin (2). However, if the irradiation is not terminated after a short period of time the lumisantonin itself rearranges into a linearly conjugated dienone (3). The dienone (3) can be isolated from the photolysis of either (1) or (2) in benzene or ether. In nucleophilic solvents (alcohol or water) the dienone (3) is also photo-chemically active and is further converted into an ester or an acid (photo-santonic acid) (4). 

Aldol reactions provide a valuable synthetic method for forming carbon-carbon bonds. They can be adapted to extend the length of a carbon chain, to form cyclic compounds, and to provide intermediates that can be transformed into more useful materials. An important feature of these intermediates is that functional groups useful for later reactions are located close to or on the carbons of the newly formed C-C bond. There is an almost bewildering number of variations on the aldol reaction and we shall not mention all of them. The main thing to recognize in all of these reactions is that the acceptor molecule always is a carbonyl compound, best an aldehyde, sometimes a ketone, even an ester (see Section 18-8E). The donor molecule is some type of carbanion usually, but not always, an enolate anion. However, any substance that has a... 

This rearrangement converts an a-halo ketone, e.g. (34), into an unstable cyclopropanone (35) which decomposes (36) into an ester (37). In the decomposition (36) the more stable carbanion acts as the leaving group. 

The chemical properties of acetoacetic ester are those of a ketone and an ester. It contains, however, a small proportion of the tautomeric enol form of the compound, as a color is produced when it is treated with ferric chloride. The ester dissolves in alkalies owing to the formation of a soluble sodium salt. It is believed that the salt is formed as the result of the interaction of the alkali with that part of the ester which has the enol structure, As the latter is removed in this way the keto form undergoes rearrangement to the enol form in order to establish the normal equilibrium between the two forms. The change continues until, in the end, the ester dissolves completely. When an aqueous solution of the sodium salt of acetoacetic ester is treated with an acid, the enol form of the ester is first precipitated in drops these slowly disappear as a result of their transformation into the keto form provided enough water is present. The solubility of the enol form in water is much less than that of the keto form (0.5 per cent and 11 per cent, respectively, at 0°). 

It consists in the transformation of an aldehyde or a ketone into an unsaiuratcd nitrile or ester, by condensing them with a phosphonate in the presence of strong bases Fi w e 2i) [184] such as hydrotalcite exchanged with tBuOK [275] or Ba(OH)j [76, 276, 277]. 

This transformation involves reduction of an ester to form an alcohol. Recall that lithium aluminum hydride (LAH) can be used to accomplish this type of reaction. However, under these conditions, the ketone moiety will also be reduced. The problem above requires reduction of the ester moiety without also reducing the ketone moiety. To accomplish this, a protecting group can be used. The first step is to convert the ketone into an acetal ... 

Baeyer-Villiger oxidation (Sect. 20.11) A reaction in which a ketone is treated with a peroxy acid and is converted into an ester via the insertion of an oxygen atom. 

Now let s draw the forward scheme. Oxidation of a secondary alcohol gives a ketone, which is then converted into an ester via a Baeyer-Vilhger oxidation (this process inserts an oxygen atom between the carbonyl group and the more substituted alkyl group). Finally, acid-catalyzed hydrolysis of the ester gives Ae desired carboxylic acid. 

As mentioned so many times throughout this entire course, there are almost always multiple correct solutions to a synthesis problem. For example, in this case, the desired transformation can be achieved using several reactions from previous chapters. The starting ketone can be converted into an ester via a Baeyer-Villiger oxidation, followed by hydrolysis to give propanoic acid. This acid can then be converted to an acid chloride upon treatment with thionyl chloride, followed by conversion to the product upon treatment with lithium dipropyl cuprate ... 

Active methylene or methine compounds, to which two EWGs such as carbonyl, alko.xycarbonyl, formyl, cyano, nitro, and sulfonyl groups are attached, react with butadiene smoothly and their acidic hydrogens are displaced with the 2,7-octadienyl group to give mono- and disubstituted compounds[59]. 3-Substituted 1,7-octadienes are obtained as minor products. The reaction is earned out with a /3-keto ester, /9-diketone, malonate, Q-formyl ketones, a-cyano and Q-nitro esters, cya noacetamide, and phenylsulfonylacetate. Di(octadienyl)malonate (61) obtained by this reaction is converted into an... 

Organic solutions can be obtained in high yield by extracting HOCl from Cl -containing aqueous solutions into polar solvents such as ketones, nitriles or esters. Electrodialysis using semiper-meable membranes affords an alternative route. 

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