Transesterifications, 3-keto ethyl esters/alcohols

Miscellaneous Uses. NCS catalyzes the transesterification of 8-keto ethyl esters with substrate alcohols under neutral conditions in refluxing toluene in excellent yields. The ethanol formed during the reaction is removed by distillation. Surprisingly, the reaction conditions are selective and the chlorination of allylic positions or olefins is not observed. Additionally, the reaction proceeds with only 1 equiv of the substrate alcohol allowing for complex esters to be readily formed (eq 26). ... 

Preferential esterification. Startg. tricarboxylic acid and Amberlyst 15 in methanol stirred at room temp, for 10 h monomethyl ester. Y 80%. a,p-Unsatd. and ar. carboxyl groups were left unaffected the method failed with higher alcohols (/-PrOH /-BuOH). Under these mild conditions, a-epimerization, c/5-tra 5-rearrangement, and transesterification (of ethyl esters) are avoided, and keto and olefinic groups remain intact. F.e. inch methyl esters of bile acids s. M. Petrini et al., Synth. Commun. 18, 847-53 (1988). 

Table 11 Transesterification reactions of -keto esters with alcohols. Reactions were carried out with ethyl acetoacetate at 110°C with toluene as the solvent and continuous azeotropic removal of alcohof...

Vinyl alcohol monomer does not exist because its keto tautomer is much more stable. Poly(vinyl alcohol) can be prepared from either poly(vinyl ester)s or from poly(vinyl ether)s. Commercially, however, it is prepared exclusively from poly(vinyl acetate). The preferred procedure is through a transesterification reaction using methyl or ethyl alcohols. Alkaline catalysts yield rapid alcoholyses. A typical reaction employs about 1% sodium methoxide and can be carried to completion in one hour at 60 °C. The product is contaminated with sodium acetate that must be removed. The reaction of transesterification can be illustrated as follows ... 

The acid-catalyzed transesterification of a /3-keto ester with another alcohol is a difficult functional group inter-conversion. However, a catalytic amount of anhydrous CUSO4 promotes smooth transesterification of methyl or ethyl /3-keto esters with primary, secondary, and tertiary alcohols (eq 17). ... 

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