Carboxylic esters monoesters

The cyclopropane cyclizations by elimination of triflinic acid (CF3S02H) are readily effected by basic treatment of triflones (trifluoromethyl alkyl sulfones) with activated /-protons (equations 46 and 47)39. The cyclopropane diesters 45 are formed on treatment of 44 with potassium hydride in DMSO or sodium methoxide in methanol (equation 48). In contrast, the monoester 46 failed to give the desired cyclopropane40. Addition of carbanions derived from /f, y-unsaturated phenyl sulfones to a, /i-unsaturated carboxylic esters and subsequent elimination of benzenesulfinate ion give cyclopropanes possessing the unsaturated side chain and the ester function in trans positions (equation 49)41. 

Many enzymes form covalent bonds with their substrates during catalysis, such as the acyl-enzyme intermediate in carboxyl ester hydrolysis (Scheme 2.1) or the glycol monoester intermediate in epoxide hydrolysis (Scheme 2.85). Despite the covalent enzyme-substrate bond, such species are metastable and should be regarded as activated intermediates . Some enzymes utilize cofactors, such as... 

Acyclic acid anhydrides react with alcohols (phenols) to give esters and carboxylic acids acid esters (monoesters) are formed from cyclic anhydrides ... 

For most cases, common fluoroacyl derivatives are sufficiently reactive and selective Thus conversion of perfluoroglutaric dichloride to a monomethyl ester by methanol proceeds smoothly under the appropriate reaction conditions [17] (equation 9) Perfluorosuccinic acid monoester fluoride, on the other hand, is prepared most conveniently from perfluorobutyrolacetone (equation 10) Owing to the strong acidity of a fluorinated carboxylic acids, Fischer esten-ficaiton with most aliphatic alcohols proceeds autocatalytically [79 20]... 

HO A phosphoric acid monoester HO A phosphoric acid diester 0 1 R" A phosphoric acid triester A carboxylic acid ester... 

Fig. 8.4. Postulated mechanism of the base-catalyzed activation of (2-oxo-l, 3-dioxol-4-yl)methyl ester prodrugs (8.62) of carboxylic acids [74] [75]. After hydrolysis, the pro-moiety is liberated as a nonisolatable carbonate monoester intermediate, which is decarboxylated rapidly to a diketone.

M). Large rate enhancements occur for base hydrolysis of the complexes, ranging from 104 with Ni° to 106 with Cu11. A pH-independent reaction occurs with the phthalate monoester due to intramolecular nucleophilic attack by the neighbouring carboxylate group leading to rate enhancements of 102-104. Metal ion-promoted water hydrolysis was also observed with these esters. 

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