Ester synthesis acid catalyzed

In his cephalosporin synthesis methyl levulinate was condensed with cysteine in acidic medium to give a bicyclic thiazolidine. One may rationalize the regioselective formation of this bicycle with the assumption that in the acidic reaction mixture the tMoI group is the only nucleophile present, which can add to the ketone. Intramolecular amide formation from the methyl ester and acid-catalyzed dehydration would then lead to the thiazolidine and y-lactam rings. The stereochemistry at the carboxylic acid a-... 

An asymmetric synthesis of 3,4,5-trisubstituted-tetrahydro-l-benzazepines has been reported based on a type a ring construction process mediated by triethylaluminium with a chiral amino ester followed by lactam reduction with borane <2006OL2667>. Dynamic thermodynamic resolution in a lithiation-substitution sequence was integral to the preparation of the amino ester. An acid-catalyzed ring construction approach to the asymmetric synthesis of 4,5,6-trisubstituted- and 3,4,5,6-tetrasubstituted azepanes based on chiral acyclic precursors has also been described <2006JA2178>. 

Lactonization of a b,i-unsaturaled ester/ In a projected synthesis of quassinoid diterpenes, the final step involves lactonization of the unsaturated ester 1. Acid-catalyzed solvolysis (HCl in THE) or treatment with an arvlsulfonic acid in toluene results mainly... 

Carboxylic acids with a carbonyl group at the 3-position decarboxylate when they are heated. Carboxylic acids can be prepared by a malonic ester synthesis the a-carbon of the diester is alkylated and the a-substituted malonic ester undergoes acid-catalyzed hydrolysis and decarboxylation ... 

Application of the above principles to the synthesis of 1,3-diselenolylium ions has been successful. iVjA -Dialkyldiselenocarbamates as their oxo esters (30) undergo acid-catalyzed cyclization and dehydration to give the cation (31) in nearly 90% yield (75JOC746, 77CC505, 80CC866, 80CC866). 

The finding that the anthelmintic thiazoloimidazole levamisole showed immunoregulatory activity spurred further investigation of this heterocyclic system. Synthesis of a highly modified analogue starts by displacement of bromine in keto ester 149 by sulfur in substituted benzimidazole 148. Cyclization of the product (150), leads initially to the carbinol 151. Removal of the ester group by saponification in base followed by acid-catalyzed dehydration of the carbinol affords the immune regulator tilomisole (152) [28]. 

Esters can also be synthesized by an acid-catalyzed nucleophilic acyl substitution reaction of a carboxylic acid with an alcohol, a process called the Fischer esterification reaction. Unfortunately, the need to use an excess of a liquid alcohol as solvent effectively limits the method to the synthesis of methyl, ethyl, propyl, and butyl esters. 

Step 3 of Figure 29.12 Oxidation and Decarboxylation (2K,3S)-lsocitrate, a secondary alcohol, is oxidized by NAD+ in step 3 to give the ketone oxalosuccinate, which loses C02 to givea-ketoglutarate. Catalyzed by isocitrate dehydrogenase, the decarboxylation is a typical reaction of a /3-keto acid, just like that in the acetoacetic ester synthesis (Section 22.7). The enzyme requires a divalent cation as cofactor, presumably to polarize the ketone carbonyl group. 

As noted in the preceding section, one of the most general methods of synthesis of esters is by reaction of alcohols with an acyl chloride or other activated carboxylic acid derivative. Section 3.2.5 dealt with two other important methods, namely, reactions with diazoalkanes and reactions of carboxylate salts with alkyl halides or sulfonate esters. There is also the acid-catalyzed reaction of carboxylic acids with alcohols, which is called the Fischer esterification. 

Scheme 8.15. Synthesis of Ketones, Esters, Carboxylic Acids, and Amides by Palladium-Catalyzed Carbonylation and Acylation... 

By employing anionic techniques, alkyl methacrylate containing block copolymer systems have been synthesized with controlled compositions, predictable molecular weights and narrow molecular weight distributions. Subsequent hydrolysis of the ester functionality to the metal carboxylate or carboxylic acid can be achieved either by potassium superoxide or the acid catalyzed hydrolysis of t-butyl methacrylate blocks. The presence of acid and ion groups has a profound effect on the solution and bulk mechanical behavior of the derived systems. The synthesis and characterization of various substituted styrene and all-acrylic block copolymer precursors with alkyl methacrylates will be discussed. 

The kinetics of the acid-catalyzed esterification reaction of 2,4,6-trimethylbenzoic acid in i-PrOH under microwave irradiation have been investigated [84], A simple and practical technique for MW-assisted synthesis of esters has been reported wherein the reactions are conducted either on solid mineral supports or by using a phase transfer catalyst (PTC) in the absence of organic solvents [85], The esterification of enols with acetic anhydride and iodine has also been recorded [86],... 

---