Ketones hydroxycarboxylic acid

A concerted mechanism is also possible for a-hydroxycarboxylic acids, and these compounds readily undergo oxidative decarboxylation to ketones.281... 

Oxidation of cyclic ketones by H2O2 in the presence of an acid zeolite was used for the preparation of lactones and u-hydroxycarboxylic acids [124]. Thus, for c-pentanone oxidation in the presence of H-ZSM-5, -valerolactone is obtained with 62.3% selectivity at 40% conversion, whereas 5-hydroxy-pentoic acid is obtained with 34% yield in the presence of Zeolon M. 

The electrocarboxylation of aldehydes and ketones leads to the corresponding a-hydroxycarboxylic acids that can easily be converted into carboxylic acids via a hydrogenation reaction [7]. It has been reported that the electrocarboxylation of aromatic ketones occurs through the reaction of C02 onto the activated carbon atom of the carbonyl group of the ketyl radical anion generated upon electron transfer to the ketone [7]. Otherwise, the aforementioned intermediate is likely to be a resonance hybrid (see Equation 12.23), and its electrophilic reaction with C02 may take place both at the carbon or the oxygen atom [42, 43]. 

An aldol addition involves the addition of the a-C atom of a carbonyl compound, a carboxylic acid, a carboxylic ester, or a carboxylic amide to the C=0 double bond of an aldehyde or a ketone. The products of aldol additions are /3-hydroxylcarbonyl compounds (aldols), /i-hydroxycarboxylic acids, /Thydroxycarboxylic esters, or j3-hydroxycarboxylic amides. 

Fig. 17.32. Oxidative cleavage of an asymmetric ketone with complementary regiose-lectivities. Lactone A is obtained by Baeyer-Villiger oxidation of menthone [2-methyl-5-(l- methylethyl)cyclo-hexanone]. Alternatively, one may first convert menthone into the silylenol ether B and cleave its C=C double bond with ozone to obtain a silyl ester containing an a-methoxyhydroperoxide group as a second functional group (which resembles the unstable structural element of the so-called ether peroxides cf. Figure 1.38). The latter is reduced with NaBH4tothe hydroxylated silyl ester C. The hydroxycarboxylic acid is obtained by acid-catalyzed hydrolysis. It cyclizes spontaneously to give lactone D.

Whilst the majority of the discussion thus far has been concerned with metallo-substituted redox molecular sieves, it is important to note that proto-nated zeolite forms can also be employed for selective oxidation with aqueous hydrogen peroxide. An excellent example of this is the study conducted by the Mobil Oil Corporation.52 Their work has shown that a number of protonated zeolites such as H-ZSM-5 or zeolite-/ can be used with hydrogen peroxide to catalyse the oxidation of cyclic ketones to lactones or the co-hydroxycarboxylic acids (Figure 4.12). 

In earlier studies, we reported remarkable rate and diastereoselectivity enhancements in allyl- and crotylborations involving a-hydroxyketones,6 a-oxocarboxylic acids7 and fi-hydroxyaldehydes and ketones, We now wish to report that fi-allyldiisopropoxyborane reacts with (3-ketoacids to produce tertiary homoallylic 13-hydroxycarboxylic acids. The reaction presumably proceeds through a bicyclic transition state (Scheme 1) to yield the desired product in good yield (Table 1). 

In the Cannizzaro reaction, the hydride ion that is being used to effect this reduction may come from an aldehyde that lacks an a-hydrogen atom, e.g. methanal or benzaldehyde. The receiving molecule may be a second molecule of the same aldehyde or a different one. The reaction requires a strong base, and the rate law is found to depend on the square of the concentration of the aldehyde and either the concentration or the square of the concentration of the base used. Overall a carboxylate anion and an alcohol are formed from two molecules of the aldehyde(s). The reaction may occur intramolecularly, i.e. a-ketoaldehydes give the a-hydroxycarboxylic acids on treatment with hydroxide ions. A variation of this process is called the Tollens reaction. In this case, a ketone or aldehyde that contains an a-hydrogen is treated with formaldehyde in the presence of Ca(OH)2. 

Kiliani method Used in carbohydrate chemistry to extend the length of the carbon chain by one carbon atom. Following the formation of a cyanohydrin of the corresponding ketone, the nitrile group is then hydrolysed to give the a-hydroxycarboxylic acid. 

Via intermediates Phenols from hydrocarbons via amines s. 1,192 a-Hydroxy ketones from ketones via a-isonitrosoketones s. 2,145 a-Hydroxycarboxylic acids from carboxylic acids via a-halogenocarboxylic acids s. 1,451 v.l. H —OH... 

Hydroxycarboxylic acid esters from cyclic ketones... 

Synthetic approaches to fluorinated p-lactones (oxetane-2-ones) are very similar to oxetane synthesis. Usually p-lactones are prepared either by cycloaddition of ketenes to aldehydes or ketones or by cyclodehydration of p-hydroxycarboxylic acids. 

Dimethyl (2/ ,3 )-tartrate provides the central C4 building block. Homer olefination is used to attach the C2 building block at one end. Asymmetric Sharpless epoxidation converts the resulting olefin to the Cg epoxide. The Cn chain, produced from the Cg and C3 building blocks, is attached at the other end. The missing Ci atom is provided by CH2N2 an Arndt-Eistert reaction leads, via the Cxg diazo ketone, to the Cjg hydroxycarboxylic acid. Cycliza-tion of the seco-isomer gives enf-100 Scheme 52). 

H202 As equal to 30. Conversion to the Baeyer-Villiger products is based on H2O2. ester represents also lactone and acid denotes hydroxycarboxylic acids formed by hydrolysis of lactones. The yields are based on the ketone consumed. Yield of lactone or ester based on the consumed hydrogen peroxide. 

Hydroxycarboxylic acid esters from ketones CO -> C(OH)-C-COOR... 

Synthesis of carboxylic acids from ketones via y -hydroxycarboxylic acid fcrf-butyl esters Modified Reformatskii synthesis... 

Ethylenecarboxylic and a-alkylideneglutaric acids from ketones via y-carbo- erf-butoxy-(5-hydroxycarboxylic acid fert-butyl esters—Synthesis with addition of 4 C atoms s. 18, 730... 

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