Palladium-catalyzed benzylation of carboxylic acids with toluene via benzylic C-H activation
Direct benzylation of carboxylic acids with toluene has been developed via palladium-catalyzed C-H acyloxylation under 1 atm of oxygen. This reaction demonstrates good functional group tolerance and high yields, providing a facile, atom-economic, and efficient method for the synthesis of benzyl esters.
Cyclopropanecarboxylic acid esters as potential prodrugs with enhanced hydrolytic stability
Esters of cyclopropanecarboxylic acid demonstrate a substantial increase in stability under both acid- and base-catalyzed hydrolytic conditions. Comparison of the stability of valacyclovir 13 with the cyclopropane analogue 14 shows that at 40 °C and pH 6 the half-life of 14 is >300 h while the value for 13 is 69.7 h. CBS-QB3 calculations on isodesmic reactions for transfer of groups from an alkane to an ester show that a cyclopropyl group provides hyperconjugative stabilization.
Bender, David M.,Peterson, Jeffrey A.,McCarthy, James R.,Gunaydin, Hakan,Takano, Yu,Houk
p. 509 - 511
(2008/09/19)
Synthesis of benzyl esters using 2-benzyloxy-1-methylpyridinium triflate
(Chemical Equation Presented) Triethylamine (Et3N) mediates esterification reactions between the title reagent (1) and carboxylic acids. Alcohols, phenols, amides, and other sensitive functionality are not affected; a dual role for Et3N as a promoter and a scavenger is postulated. Benzyl esters are obtained from substrates including amino acid and sugar derivatives.
Tummatorn, Jumreang,Albiniak, Philip A.,Dudley, Gregory B.
p. 8962 - 8964
(2008/03/12)
Direct ester condensation from a 1:1 mixture of carboxylic acids and alcohols catalyzed by hafnium(IV) or zirconium(IV) salts
To promote atom efficiency in synthesis and to avoid the generation of environmental waste, the use of stoichiometric amounts of condensing reagents or excess substrates should be avoided. In esterification, excess amounts of either carboxylic acids or alcohols are normally needed. We found that the direct condensation of equimolar amounts of carboxylic acids and alcohols could be achieved using hafnium(IV) or zirconium(IV) salts. These metal salts are highly effective as catalysts for the selective esterification of primary alcohols with carboxylic acids in the presence of secondary alcohols or aromatic alcohols. The present methods can be applied to direct polyesterification and may be suitable for large-scale operations.
Generation of esters from carboxylic acids using Appel's salt (4,5-dichloro-1,2,3-dithiazolium chloride)
Esters can be generated directly in good yields under mild conditions from the corresponding carboxylic acid and alcohol using Appel's salt (4,5-dichloro-1,2,3-dithiazolium chloride) and 2,6-lutidine.
Folmer,Weinreb
p. 2737 - 2740
(2007/10/02)
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