Categories: C-O Bond Formation >
Synthesis of esters
N-alkoxyamides conveniently afford the corresponding carboxylic esters in the presence of NBS in toluene via oxidative homocoupling and the subsequent thermal denitrogenation. Even substrates bearing a bulky or long-chain substituent gave products in good yields in this convenient and economic approach to a direct transformation of an alkoxyamide moiety into the carboxylic ester functional group.
N. Zhang, R. Yang, D. Zhang-Negrerie, Y. Du, K. Zhao, J. Org. Chem., 2013, 78, 8705-8711.
In a Cu-catalyzed aerobic oxidative esterification of simple ketones via C-C bond cleavage, various common ketones, even inactive aryl long-chain alkyl ketones, are selectively converted into esters. The reaction tolerates a wide range of alcohols, including primary and secondary alcohols, chiral alcohols with retention of the configuration and electron-deficient phenols.
X. Huang, X. Li, M. Zou, S. Song, C. Tang, Y. Yuan, N. Jiao, J. Am. Chem. Soc., 2014, 136, 14858-14865.
A one-carbon homologation of an alcohol to the extended carboxylic acid, ester, or amide involves a Mitsunobu reaction with an alkoxymalononitrile, followed by unmasking in the presence of a suitable nucleophile. The homologation and unmasking can even be performed in a one-pot process in high yield.
N. Kagawa, A. E. Nibbs, V. H. Rawal, Org. Lett., 2016, 18, 2363-2366.
In a Fe-catalyzed aerobic oxidative esterifications of arylacetonitriles, acyl electrophiles were in situ generated via chemoselective C(CO)-CN bond cleavage. Alcohols, alkoxsilanes, silicate esters, or borate esters can be acylated to the corresponding aryl esters in good to excellent yields under molecular oxygen. Dioxygen serves as both oxidant and reactant.
W. Kong, B. Li, X. Xu, Q. Song, J. Org. Chem., 2016, 81, 8436-8443.
The allylic oxidation of cyclic alkenes with a copper-aluminum mixed oxide as catalyst in the presence of a carboxylic acid and tert-butyl hydroperoxide as the oxidant gives the corresponding allylic esters. When l-proline is employed, the allylic alcohol or ketone is obtained.
A. L. García-Cabeza, R. Marín-Barrios, F. J. Moreno-Dorado, M. J. Ortega, G. M. Massanet, F. M. Guerra, Org. Lett., 2014, 16, 1598-1601
The facile and efficient conversion of a tert-butyl protecting group to an acetyl protecting group by catalytic amounts of bromine in acetyl chloride and the presence of acetic acid has been developed. The fairly mild reaction conditions are of particular interest for new protecting group strategies for sulfur functionalised target structures.
A. Blaszczyk, M. Elbing, M. Mayor, Org. Biomol. Chem., 2004, 2, 2722-2724.
Group 5 and 6 metal chlorides were found as very efficient catalysts for acylative cleavage of ethers. Compared with conventional Lewis acid catalysts, group 5 and 6 metal chlorides showed better results in the catalytic C-O bond cleavage.
Q. Guo, T. Miyaji, R. Hara, B. Shen, T. Takahashi, Tetrahedron, 2002, 58, 7327-7334.
A stereoconservative protection and deprotection method of amino and carboxyl groups includes the generation of N-Phthaloyl N'-alkyl secondary amides from N-phthaloyl amino acids by using a mixed anhydride method. These secondary amides have been transformed by thermal rearrangement of the intermediate nitrosoamides to esters with retention of configuration and excellent yields.
D. M. Shendage, R. Froehlich, G. Haufe, Org. Lett., 2004, 6, 3675-3678.