The Reactions of Esters

Esters do not react with chloride ion because it is a much weaker base than the RO group of the ester, so d (not RO ) would be the base eliminated from the tetrahedral intermediate (Table 16.1). 

An ester reacts with water to form a carboxylic acid and an alcohol. This is an example of a hydrolysis reaction. A hydrolysis reaction is a reaction with water that converts one compound into two compounds (lysis is Greek for breaking down ). 

Both the hydrolysis and the alcoholysis of an ester are very slow reactions because water and alcohols are poor nucleophiles and the RO group of an ester is a poor leaving group. Therefore, these reactions are always catalyzed when carried out in the laboratory. 

Both hydrolysis and alcoholysis of an ester can be catalyzed by acids (Section 16.10). The rate of hydrolysis can also be increased by hydroxide ion and the rate of alcoholysis can be increased by the conjugate base (RO ) of the reactant alcohol (Section 16.11). 

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The reaction of esters with Gngnard reagents and with lithium aluminum hydride both useful m the synthesis of alcohols were described earlier They are reviewed m Table 20 4 on page 848... 

Most of the reactions of ester enolates described so far have centered on stabilized eno lates derived from 1 3 dicarbonyl compounds such as diethyl malonate and ethyl ace toacetate Although the synthetic value of these and related stabilized enolates is clear chemists have long been interested m extending the usefulness of nonstabilized enolates derived from simple esters Consider the deprotonation of an ester as represented by the acid—base reaction... 

The reactions of esters have been reviewed (11—15). Because of the large number of possible acid and alcohol moieties, the chemical properties of esters may differ considerably. Only typical reactions appHcable to the majority of esters are described in the following sections. 

The reaction of esters with Gr-ignard reagents and with lithium aluminum hydride, both useful in the synthesis of alcohols, were described earlier. They are reviewed in Table... 

Specificity is not always perfect. Sometimes an enzyme will work with any member of a class of compounds. For example, some esterases (enzymes that catalyze the reaction of esters with water) will work with numerous esters of similar, but different, structures. Usually, in cases of this kind, one of the members of the substrate class will react faster than the others, so the rates will vary from one substrate to another. 

A novel chiral dissymmetric chelating Hgand, the non-stabiUzed phosphonium ylide of (R)-BINAP 44, allowed in presence of [Rh(cod)Cl]2 the synthesis of a new type of eight-membered metallacycle, the stable rhodium(I) complex 45, interesting for its potential catalytic properties (Scheme 19) [81]. In contrast to the reactions of stabihzed ylides with cyclooctadienyl palladium or platinum complexes (see Scheme 20), the cyclooctadiene is not attacked by the carbanionic center. Notice that the reactions of ester-stabilized phosphonium ylides of BINAP with rhodium(I) (and also with palladium(II)) complexes lead to the formation of the corresponding chelated compounds but this time with an equilibrium be-... 

The 2,5-dihydro-l,2-oxaphosphole-2-oxide derivatives 196 were also obtained from the reaction of esters of 3-chloro-4-methyl-l,3-pentadiene-2-phosphonic acid with halogens (Scheme 78) [155, 156],... 

Ester aminolysis, in general, occurs under harsh conditions that require high temperatures and extended reaction periods or the use of strong alkali metal catalysts. An efficient solid state synthesis of amides from nonenolizable esters and amines using KO Bu under the action of microwave irradiation [97] has been described. The reaction of esters with octylamine was extensively studied to identify possible micro-wave effects [98] (Eq. (45) and Tab. 3.20). 

In this chapter no attempt is made to present an exhaustive compilation of the reactions of esters containing phosphorus. For a more extensive survey the references on p. 216 should be consulted. 

Several papers have been devoted to the subject of reactions of phosphoranes with carboxylic acids and their derivatives. Thus triphenylphosphine dibromide (111) in acetonitrile cleaves lactones,93 while the corresponding dichloride (112) converts esters into acid chlorides.94 The reactions of esters with phosphorus pentachloride (101) have been studied further,95 and the influence of structural changes on the yields of products (113) and (114) has resulted in minor modifications to the mechanism previously96 outlined. 

The best known example of the treatment of a primary aliphatic amine with nitrous acid involves the reaction of esters of glycine hydrochloride with sodium nitrite to form esters of diazoacetic acid. This reaction is carried out at low temperatures and under such reaction conditions that any IV-nitroso primary amine which might have been formed is immediately converted to the diazoacetate [15, 16]. Treatment of 1-methyl-2,2,2-trifluoroethylamine hydrochloride, another primary amine, with sodium nitrite in an aqueous system also evidently leads to the corresponding diazoalkane [17]. 

The dinuclear catalyst 21-Ba2, in which the azacrown ether units are linked to vicinal positions of the calix 4 arcnc scaffold, is not only superior to its diagonal regioisomer 22-Ba2 in all cases, but is also superior to 17-Ba2 in the reactions of esters 14, 23, and 24. Modest levels of cooperation between metal ions are seen in the catalyzed reactions of the longest substrate 25, which indicates that dinuclear complexes cannot expand their intermetal distances to adapt to the long carboxylate-carbonyl distance in 25. 

Alcohols can also be generated by hydride reduction of esters of support-bound alcohols or thiols [396,655,656], or by reduction of resin-bound imides (Table 3.35). Similarly, the reaction of esters of support-bound alcohols or thiols with Grignard or... 

Olefination of carbonyl compounds and the reaction of esters with activated thiols such as Al(SPh)3 [65] or Me2AIS(CH2)n SAIIV [66]... 

General procedure for the reactions of esters with Lawesson s reagent... 

The reactions of esters of ,/i-unsatu rated acids with a 1.5 fold excess of amines were carried out without a solvent in a commercial microwave oven (Funai M0785VT) in a reaction vessel for several minutes. The power of microwave irradiation depends on the stability of the starting compound under microwave irradiation conditions. The Michael adduct was separated from the unreacted starting substances by column chromatography on silica gel with a hexane-ethyl acetate mixture (2 1) as the eluent. 

The reactions of esters of trans-(S)-la with amines 2a-c were carried out in a commercial microwave oven (Funai MO 785 VT) in the absence of solvent for 12 min at a power of 510 W and the temperature of the reaction mixture not higher than 60 °C. The reaction run was monitored by thin layer chromatography on silica gel, and reaction products were isolated by column chromatography on silica gel using a heptane-ethyl acetate (2 1) mixture as the eluent. 

The l-hydroxybicyclo[ .1.0] system is obtained by the reaction of esters bearing a terminal double bond [123]. The hydroxycyclopropanation of the unsaturated ester... 

Hamell, M. Levine, R. Condensations effected by the alkali amides. IV. The reactions of esters with lithium amide and certain substituted lithium amides. J. Org. Chem. 1950, 35, 162-168. 

If we treat alkoxycarbcne complexes not with phosphines but with primary or secondary amines, we observe a new kind of reaction, reminiscent of the reactions of esters. This observation led us into peptide chemistry along a path that proved to be quite surprising to a coordination chemist. We could show that the alkoxy group of alkoxy(organo) carbene complexes can be substituted not only by mono- or dialkylamino residues but also by free amino groups of amino acid and peptide esters (63, 64). The principle of this reaction is shown in Scheme 2. 

Scheme 9.2. Representations of potential randomly constructed networks via the reaction of ester terminated dendrimer and amine terminated dendrimer.

As shown earlier (Figure 13.22), silyl ketene acetals can be prepared at -78 °C by the reaction of ester enolates with chlorosilanes. O-Allyl-O-silyl ketene acetals (A in Figure 14.48) are formed in this reaction if one employs allyl esters. Silyl ketene acetals of type A undergo [3,3]-rearrangements rapidly upon warming to room temperature. This variation of the Claisen rearrangement is referred to as the Ireland-Claisen rearrangement. 

The reaction of esters with sodium in ethanol is referred to as the Bouveault-Blanc reaction. Prior to the discovery of complex metal hydrides, this reaction was the only method for the reduction of esters to alcohols. The diesters shown in Figure 17.59 produce a diol in this way. 

A novel variation of a double dehydrohalogenation leading to a cyclopropene is the reaction of ester 75 with base176 ... 

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