Carbonic acid diester derivative

The chemical diversity of carboxylic acid esters (R-CO-O-R ) originates in both moieties, i.e., the acyl group (R-CO-) and the alkoxy or aryloxy group (-OR7). Thus, the acyl group can be made up of aliphatic or aromatic carboxylic acids, carbamic acids, or carbonic acids, and the -OR7 moiety may be derived from an alcohol, an enol, or a phenol. When a thiol is involved, a thioester R-CO-S-R7 is formed. The model substrates to be discussed in Sect. 7.3 will, thus, be classified according to the chemical nature of the -OR7 (or -SR7) moiety, i.e., the alcohol, phenol, or thiol that is the first product to be released during the hydrolase-catalyzed reaction (see Chapt. 3). Diesters represent substrates of special interest and will be presented separately. 

Carbonic acid esters (alkoxycarbonyl derivatives) are diesters of general formula R-O-CO-O-R. A single mechanism operates in the HO -catalyzed (and presumably also in the enzyme-catalyzed) hydrolysis of carbonic acid esters, namely a rate-determining addition of the base to the carbonyl C-atom to form an intermediate whose breakdown yields the drug (ROH), C02, and an alcohol (R OH) (Fig. 8.7,a) [153],... 

Although carbonic acid itself is always in equilibrium with carbon dioxide and water, it has several important stable derivatives. Carbonate esters are diesters of carbonic acid, with two alkoxy groups replacing the hydroxyl groups of carbonic acid. 

These too are made by carbonyl substitution reactions, but this time the nucleophile is aromatic and the electrophile is an aliphatic derivative of carbonic acid such as phosgene (COCI2) or a carbonate diester [CO(OR)2]. The aromatic nucleophile is a diphenol but the two OH groups are on separate rings joined together by an electrophilic aromatic substitution. This compound is called bisphenol A and has many other applications. 

In a study by Berti et al., acid-catalyzed hydrolysis of styrene oxide was reported to occur with 67% inversion and 33% retention at the benzyl carbon.45 In a later study, it was reported that the styrene glycol product formed in the acid-catalyzed hydrolysis of chiral styrene oxide is completely racemic, which would indicate an A-l mechanism.46 As these two results indicate quite different mechanisms for this reaction, the glycol product from acid-catalyzed hydrolysis of chiral styrene oxide was converted to its bis-( + )-a-(methoxy-a-trifluoromethyl)phenylacetate diester derivative, and the composition of the diastereomeric diester mixture was determined by H NMR.47 This study agreed with those of Berti et al. and showed that acid-catalyzed hydrolysis of styrene oxide occurs with 67% inversion and 33% retention at the benzyl carbon. Acid-catalyzed methanolysis of styrene oxide is reported to occur with 89% inversion at the benzyl carbon.48 The fact that the diol product from acid-catalyzed hydrolysis of chiral styrene oxide is not completely racemic demonstrates that the lifetime of the carbocation is not sufficiently long for it to become symmetrically solvated. 

Carbonic acid (H2CO3) is formed when carbon dioxide dissolves in water. Although carbonic acid itself is always in equilibrium with carbon dioxide and water, it has several important stable derivatives. Carbonate esters are diesters of carbonic acid, with two alkoxy groups replacing the hydroxyl groups of carbonic acid. Ureas are diamides of carbonic acid, with two nitrogen atoms bonded to the carbonyl group. The unsubstituted urea, simply called urem, is the waste product excreted by mammals from the metabolism of excess protein. Carbamate esters (urethanes) are the stable esters of the unstable carbamic acid, the monoamide of carbonic acid. 

Carbonates can be described as diester derivatives of carbonic acid, formed by condensation with hydroxyl compounds. However, carbo q lic acids do not possess the necessaiy reactivity to synthesize such products. Therefore bifunctional reactive molecules such as phosgene or carbonyldiimidazoles like N,N -carbonyldiimidazole (CDI) and disuccinimidyl carbonate (DSC) are commonly used (Scheme 1.13). These compounds readily react with nucleophiles to form stable conjugates. They react with hydro)q l-containing molecules to form the amino-reactive carbonate or carbamate intermediates. These intermediates react in a subsequent step with primaiy amines to form stable carbamate bonds (aliphatic urethanes). The reaction is usually carried out in alkaline media (pH 7-9) and in the absence of competing amino and... 

The reaction of cycloheptaamylose with diaryl carbonates and with diaryl methylphosphonates provides a system in which a carboxylic acid derivative can be directly compared with a structurally analogous organo-phosphorus compound (Brass and Bender, 1972). The alkaline hydrolysis of these materials proceeds in twro steps, each of which is associated with the appearance of one mole of phenol (Scheme Y). The relative rates of the two steps, however, are reversed. Whereas the alkaline hydrolysis of carbonate diesters proceeds with the release of two moles of phenol in a first-order process (kh > fca), the hydrolysis of methylphosphonate diesters proceeds with the release of only one mole of phenol to produce a relatively stable aryl methylphosphonate intermediate (fca > kb), In contrast, kinetically identical pathways are observed for the reaction of cycloheptaamylose with these different substrates—in both cases, two moles of phenol are released in a first-order process.3 Maximal catalytic rate constants for the appearance of phenol are presented in Table XI. Unlike the reaction of cycloheptaamylose with m- and with p-nitrophenyl methylphosphonate discussed earlier, the reaction of cycloheptaamylose with diaryl methylphosphonates... 

The 7-azabicyclo[2.2.1]heptene derivative (57) decomposes in hot aqueous sodium carbonate solution to give A-benzylpyrrole-3,4-dicarboxylic acid and, presumably, ethylene. Furan-3,4-dicarboxylic acid derivatives are formed analogously on heating the 7-oxabicyclo-[2.2.1]heptene diesters (58). The only thermal decomposition of a... 

Due to the complexity of conformational equilibria, the application of the dibenzoate chirality rule to determination of the absolute configuration of acyclic diols and polyols requires cautious evaluation of the CD data. For example, (0,0)-dibenzoyl derivatives of diesters and N.N.N ,AT-tetraalkyldiamides of (/t,f )-tartaric acid give exciton Cotton effects of opposite sign due to the preference of diesters for a planar and tetraalkyldiamides for a gauche conformation of the carbon chain176. 

The synthesis of succinic acid derivatives, /3-alkoxy esters, and a,j3-unsaturated esters from olefins by palladium catalyzed carbonylation reactions in alcohol have been reported (24, 25, 26, 27), but full experimental details of the syntheses are incomplete and in most cases the yields of yS-alkoxy ester and diester products are low. A similar reaction employing stoichiometric amounts of palladium (II) has also been reported (28). In order to explore the scope of this reaction for the syntheses of yS-alkoxy esters and succinic acid derivatives, representative cyclic and acyclic olefins were carbonylated under these same conditions (Table I). The reactions were carried out in methanol at room temperature using catalytic amounts of palladium (II) chloride and stoichiometric amounts of copper (II) chloride under 2 atm of carbon monoxide. The methoxypalladation reaction of 1-pentene affords a good conversion (55% ) of olefin to methyl 3-methoxyhexanoate, the product of Markov-nikov addition. In the carbonylation of other 1-olefins, f3-methoxy methyl esters were obtained in high yields however, substitution of a methyl group on the double bond reduced the yield of ester markedly. For example, the carbonylation of 2-methyl-l-butene afforded < 10% yield of methyl 3-methyl-3-methoxypentanoate. This suggests that unsubstituted 1-olefins may be preferentially carbonylated in the presence of substituted 1-olefins or internal olefins. The reactivities of the olefins fall in the order RCH =CHo ]> ci -RCH=CHR > trans-RCH =CHR >... 

A CH-group, which bears vinyl and sulfide substituents, is acidic enough to be metallated by strong bases. Other d3-synthons may contain two activating functional groups in Imposition ( homoenolate -equivalents). Only one of the a-carbons is deprotonated under appropiate conditions (e.g. succinic diesters). Ano ther possibility is an acidic carbon and a non-acidic functional group in 1,3-positions (e.g. propargyl derivatives). Silyl ethers of a, -unsaturated alcohols can also be converted to anions, which react as d3-synthons (W. Oppolzer, 1976). 

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