Hydroxycarboxylic acid esters lactones

Reaction with Lactones, Hydroxycarboxylic acid ester complexes of titanium are formed by reaction of a tetraalkyl titanate with a lactone, such as p-propiolactone, y-butyrolactone, or valerolactone (35). For example,... 

Mukaiyama developed l-alkyl-2-halopyridinium salts, which are useful reagents for the preparation of carboxylic esters and lactones in the presence of tertiary amines [22]. After generation of activated onium salts from the corresponding co-hydroxycarboxylic acids, spontaneous lactonization smoothly proceeds to produce various macrolactones. Bartlett first used this lactonization method for the... 

Later, Dale-followed by Kricheldorf-observed the presence of carbon-carbon double bonds at the extremities of polymers formed in the so-performed polymerization of P-lactones [39, 40]. According to experimental results [41, 42], the initiation involved a nucleophilic attack at the carbonyl carbon atom of a monomer by the alkoxide anion of the initiator, cleaving the acyl-oxygen bond to yield the corresponding potassium alkoxide of the respective P-hydroxycarboxylic acid esters (Scheme 9.12). The acidic a-proton abstraction involved the formation of an unsaturated ester due to KOH elimination. Finally, polymerization occurred in the case involving P-lactone in excess, with the KOH acting as initiator. 

In lipase-catalyzed ROP, it is generally accepted that the monomer activation proceeds via the formation of an acyl-enzyme intermediate by reaction of the Ser residue with the lactone, rendering the carbonyl more prone to nucleophilic attack (Fig. 3) [60-64, 94]. Initiation of the polymerization occurs by deacylation of the acyl-enzyme intermediate by an appropriate nucleophile such as water or an alcohol to produce the corresponding co-hydroxycarboxylic acid or ester. Propagation, on the other hand, occurs by deacylation of the acyl-enzyme intermediate by the terminal hydroxyl group of the growing polymer chain to produce a polymer chain that is elongated by one monomer unit. 

Reactions of hydroxycarboxylic acids, HO(CHj) COOH, also depend on value of n. In acid solutions, y-hydroxycarboxylic acid (n = 3) and 8-hydroxycarboxylic acid (n = 4) form cyclic esters (lactones) with, respectively, five-membered and six-membered rings. 

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.

L-ascorbic acid (Figure 9-9) is a lactone (internal ester of a hydroxycarboxylic acid) and is characterized by the enediol group, which makes it a strongly reducing compound. The D form has no biological activity. One of the isomers, D-isoascorbic acid, or erythorbic acid, is produced commercially for use as a food additive. L-ascorbic acid is readily and reversibly oxidized to dehydro-L-ascorbic acid (Figure 9-10), which retains vitamin C activity. This compound can be further oxidized to diketo-L-gulonic acid, in a... 

Under Fischer esterification conditions, many hydroxycarboxylic acids i intramolecular esters (lactones). ... 

Mesocyclic lactones. Cyclization of w-hydroxycarboxylic acids via the 0,0 -disilyl intermediates is applicable to medium-sized rings (7-membered, 35% 8- to 13-membered, 79-88%). An initial silyl carboxylate formation step is catalyzed by (Ph3P)3RhCl at room temperature which is followed by an intramolecular 0-silylation at 80°. Elimination of l,l,3,3-tetramethylbenzo-2,l,3-oxadisilazole occurs when the cyclic silylether/esters are exposed to MejSiiOTf). ... 

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. 

Polyesters contain the ester group —COO— in the main chain. Many methods are suitable for their synthesis self-condensation of a,o>-hydroxy acids, ring-opening polymerization of lactones, the polycondensation of dicarboxylic acids with diols, transesterification, the polycondensation of diacyl chlorides with diols, polymerization of O-carboxy anhydrides of a- and jS-hydroxycarboxylic acids, and the copolymerization of acid anhydrides with cyclic ethers. The last reaction is commercially used in the curing of epoxides with anhydrides. 

Hydroxycarboxylic acids and 5-hydroxycarboxylic acids occur in the form of corresponding y- and 5-lactones in many fruits, especially apricots and peaches. Many other hydroxy fatty acids are also found in seed oils of plants. For example, (S)-jalapinolic acid (3-28) occurs in lipophilic ester-type dimers of acylated pentasaccharides derived from L-rhamnose in sweet potato Ipomoea batatas, Convolvulaceae), which are known as batatins. (9Z,12S)-12-Hydroxyoctadec-9-enoic (ricinoleic) acid (3-29) occurs in castor oil, where it represents about 90% of the total fatty acids. So-called castor oil is extracted from the seeds of the castor oil plant Ricinus communis) of the Euphorbiaceae family, and is used only for technical purposes as it has purgative properties. 

Generally, lactones with five-membered and six-membered rings are not too reactive. They are relatively stable in acidic solutions, where they typically arise by spontaneous dehydration of hydrox-ycarboxylic adds. In aqueous solutions, particularly in alkaline solutions, the lactone ring opens with the formation of a salt of the hydroxycarboxylic acid. The original lactone may result after acidification, especially on heating. Lactones react with alcohols to form esters and, similarly, the lactone ring opens on reaction with amino compounds to form amides. 

A mixture of phenylacetic acid, benzyl alcohol, and tri-n-butylamine in methylene chloride added under argon to a mixture of l-methyl-2-bromopyridinium iodide and methylene chloride, and refluxed 3 hrs. benzyl phenylacetate. Y 97%. F. e., also with l-methyl-2-chloropyridinium iodide, s. T. Mukaiyama et al., Chem. Lett. 1975, 1045 Bull. Chem. Soc. Japan 50, 1863 (1977) carboxylic acid amides from amines (cf. Synth. Meth. 26, 367) s. ibid. 1975, 1163 3,4-dihydro-2H-pyrido-[1,2-a]pyrimid-2-one as acid scavenger cf. ibid. 1976, 13, 57 lactones from hydroxycarboxylic acids (cf. Synth. Meth. 17, 320) with 2-chloropyridine methio-dide and triethylamine s. ibid. 1976, 49 esters with 2 halogeno-3-ethylbenzothia-zolium salts of ibid. 1976, 267 2-chloro-N-methylbenzothiazolium triflate as condensing agent s. F. Souto-Bachiller, G. S. Bates, and S. Masamune, Chem. Com-mun. 1976, 719. 

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