Lactones monoesters

This review aims at reporting on the synthesis of aliphatic polyesters by ROP of lactones. It is worth noting that lactones include cyclic mono- and diesters. Typical cyclic diesters are lactide and glycolide, whose polymerizations provide aliphatic polyesters widely used in the frame of biomedical applications. Nevertheless, this review will focus on the polymerization of cyclic monoesters. It will be shown that the ROP of lactones can take place by various mechanisms. The polymerization can be initiated by anions, organometallic species, cations, and nucleophiles. It can also be catalyzed by Bronsted acids, Lewis acids, enzymes, organic nucleophiles, and bases. The number of processes reported for the ROP of lactones is so huge that it is almost impossible to describe aU of them. In this review, we will focus on the more... 

Related to case is reduction of the monoester (l/ ,25)-2-methoxycarbonyl-4-oxo-l-cy-clopentanecarboxylate (see p401) followed by lactone formation to give 36 and oxidation to the known bicyclic dione 3757. Configurational assignment rests on the fact that the ester group in 35 is reduced under the reaction conditions whereas the free acid is not. Thus, reliability in correlations of this type rests on a sufficient difference in reactivity of the two functional groups under the selected conditions. 

Asymmetric ring opening of achiral monocyclic, bicyclic and tricyclic anhydrides under formation of the corresponding chiral monoesters can be accomplished in high yield with modest enantioselectivity with methanol in the presence of less than stoichiometric amounts of cinchona alkaloids in toluene or diethyl ether (Table 9)91 94. As expected the use of cinchonine A or quinidine C, and of cinchonidine B or quinine D gives opposite enantiomers. Recrystallization of the monoesters and lactones affords material of considerably higher enantiomeric purity (Table 9, entries 15, 16, 21, and 23). 

In toluene with 4 equiv methanol and a catalytic amount of the alkaloid. b ee values are determined by conversion of the monoesters to the (R)-l-(l-naphthalenyl)ethylamides (entries 1-14) and analysis by HPLC, by salt formation with (R)-l-phenylethylamine (entries 15-20) or by H-NMR spectroscopy in the presence of Eu(hfc)3. Absolute configurations are determined by chemical correlation or by X-ray analysis of the Mosher ester of the lactone alcohol (entry 21). With 20 equiv of methanol. d With 4 equiv of methanol. With 10 equiv of methanol. f With 3 equiv of methanol. 

Cyclopentanone reacts with peroxybenzoic acid to form a peroxy monoester. The alkyl group that migrates is the ring itself, leading to formation of a six-membered lactone. 

Robins and Sakdarat have achieved the first reconstruction of an eleven-membered macrocyclic pyrrolizidine diester (43).16 Treatment of (+)-retronecine (13) with 3,3-dimethylglutaric anhydride gave a mixture of the 7- and 9-monoesters of (+)-retronecine. Intramolecular lactonization of this mixture via... 

The photolysis of the 6-oxo-3a,5a-cyclo-19-oic acid (520) gives initially the 4-en-6-one (521), but in t-butanol a rapid photo-addition then affords the 4a-t-butoxy-6-hydroxy-lactone (522). Similar reactions transformed the methyl ester (523) into the ketonic derivative (525). Photolysis of the saturated keto-acid (526), in an alcohol as solvent, gave first the corresponding 6-monoester (527) of the 5,6-seco-6,19-dioic acid, and finally the 6,19-anhydride (528). Formation of the 6-ester (527) probably involves addition of the solvent alcohol to a keten intermediate. ... 

Acids, monoesters and lactones of Table 11.1-13 which can be obtained with other hydrolases as such or of opposite configuration are contained in Table 11.1-5. 

The photocatalyzed addition of 2-propanol to the chiral menthyl monoesters of maleic acid exhibits modest levels of stereoselectivity (1,4-induction)24. The reaction proceeds via 2-propanoyl radicals that add regio- and stereoselectively to the double bond. Hydrogen abstraction and subsequent lactonization gives two diastcreomeric terebic acid derivatives. 

B.V. The Stobbe Condensation. When succinic ester derivatives (such as diethyl succinate, 215) are condensed with non-enolizable ketones or aldehydes in the presence of base, the initial condensation product is 216. The alkoxide reacts with the distal ester via acyl substitution to give a lactone intermediate (217). In the original version of this reaction, saponification of 217 gave the a-alkylidene monoester, 218. The reaction is not completely general and is limited to those a, co-diesters for which the Dieckmann condensation is not a... 

Chemical resolution of a meso-elio/. Acylation of the symmetrical meyo-diol ciy-2-cyclopentene-l,4-diol (2) with 1 equiv. of the chiral reagent 1 in pyridine affords a mixture of the monoesters 3 and 4 in 517 yield, together with some of the diester. The mono esters were separated readily by fractional crystallization to give pure, optically active 3 and 4. These esters were converted into the (+ )-and ( —)-5 hydroxy ethers, respectively, and then into the optically active lactones ( + )- and (—)-6 by Claisen rearrangement and lactonization (6, 608-609). These lactones have been converted into both natural and unnatural prostaglandins. See scheme (I) at top of page 321. 

The half ester of (E -muconic acid (456) was synthesized in three steps as follows Starting from catechol (457), oxidative cleavage with a peracid led to the (Z,Z)-diacid 458, which was monoprotected via lactonization to provide compound 459, and by treatment with Eschenmoser s base the desired monoester 460 was obtained (Scheme 8.15). 

Lactones from dicarboxylic acid monoesters COOH - CH2OH... 

Other major lipid classes in the fatty acyl category include fatty add esters, such as wax monoesters and diesters and the lactones. The fatty ester class also has subclasses that include important biochemical intermediates, such as fatty acyl thioester-CoA derivatives, fatty acyl thioester-acyl carrier protein (ACP) derivatives, fatty acyl carnitines (esters of carnitine), and fatty adenylates, which are mixed anhydrides. Fatty alcohols, fatty aldehydes, and fatty amides represent further subclasses, the last sometimes showing interesting biological activities in various organisms. 

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