Methyl ester, aromatic, cleavage

Lignin ozonation products contain some diacids that occur in nonesterified, partially esterified, and fully esterified forms (typically methyl esters derived from cleavage of the methoxylated aromatic rings). Bonnet et al. (1989) chose to esterify the free carboxyl groups by use of diazomethane to simplify the... 

Diels-Alder addition of tetrachlorocyclopentadiene dimethylketal to endo-5-norbornene carboxylic acid produces (459). Ketal cleavage (H2SO4), cheletropic loss of CO (reflux in o-dichloro benzene), and aromatization (bromine in hot chlorobenzene) affords the endo-acid (460 X = Cl) which can be dechlorinated by reaction with Ni-Al alloy and alkali to give (460 X = H). The clean retention of stereochemistry in reaction sequence is suggested to be of value in the general synthesis of alicyclic-substituted benzonorbornenes the methyl ester of (460 X = H) can likewise be prepared without epimerization. ... 

Esters of aromatic acids in aprotic solvents form radical-anions detected by cyclic voltammetry on a short time scale [144]. Ethyl benzoate has E° = -2,19 V V5. see [145], Follow-up reactions of radical-anions from methyl and ethyl benzoate result from protonation by extraneous water. rm-Butyl benzoate radical-anion undergoes very rapid cleavage of the alkyl-oxygen bond to give benzoate ion and rerf-butyl radical. 

Fig. 2.2. Cleavage of aromatic methyl ether using Sn2 reactions. In the dipolar aprotic solvent DMF, thiolate and chloride ions are particularly good nucleophiles for want of solvation through hydrogen bonding. In pyri-dinium hydrochloride a similar effect occurs because for each chloride only one N5 —H5 group is available for hydrogen bonding. The same increase in nucleophilicityin a dipolar aprotic solvent is used to cleave /i-ketomethyl esters with lithium iodide in DMF (cf. Figure 13.29).

A convenient method for preparing alicyclic or aromatic methyl ketones consists in the acylation of the ethoxymagnesium derivative of diethyl malonate with the appropriate acyl chloride, followed by acid hydrolysis and decarboxylation of the resulting /3-keto diester. The last step is Carried out like the ketonic cleavage of /3-keto esters. The over-all yields are 60-85%. 

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