The electronic effects of tetranuclear zinc cluster catalysts on transesterification were investigated by changing the carboxylate ligands in the clusters. High catalyst activity crucially depended on the balance between Lewis acidity and Brønsted basicity of the catalyst; this was consistent with the dual activation of both the electrophile and nucleophile by the cooperative zinc centers. In addition
Cesium Carbonate Catalyzed Esterification of <i>N</i>-Benzyl-<i>N</i>-Boc-amides under Ambient Conditions
作者:Danfeng Ye、Zhiyuan Liu、Hao Chen、Jonathan L. Sessler、Chuanhu Lei
DOI:10.1021/acs.orglett.9b02513
日期:2019.9.6
We report a general activated amide to ester transformation catalyzed by Cs2CO3. Using this approach, esterification proceeds under relatively mild conditions and without the need for a transition metal catalyst. This method exhibits broad substrate scope and represents a practical alternative to existing esterification strategies. The synthetic utility of this protocol is demonstrated via the facile synthesis of crown ether derivatives and the late-stage modification of a representative natural product and several sugars in reasonable yields.
Oxyfunctionalization of Aliphatic Esters by Methyl(trifluoromethyl)dioxirane
作者:Gregorio Asensio、Gloria Castellano、Rossella Mello、M. E. González Núñez
DOI:10.1021/jo9604189
日期:1996.1.1
The oxidation of lineal, cyclic, and bicyclic aliphatic p-chlorobenzoic and p-chorobenzenesulfonic acid esters 2 with methyl(trifluoromethyl)dioxirane (TFDO) (1) occurs at positions in the hydrocarbon chain distant from the directing group with a significant degree of selectivity to give the corresponding keto or hydroxy esters. Compounds 2 are relatively deactivated with respect to this oxidation due to the electron-withdrawing nature of the ester moiety. Methylene C-alpha-H and C-beta-H bonds remain unchanged in all cases, but tertiary C-beta-H bonds undergo oxidation with TFDO (1). Stereoelectronic factors are used to explain the faster reaction rate in competition experiments for the oxidation of endo-norbornyl ester 2h than for its exo-isomer 2g.