Categories: C-O Bond Formation > Synthesis of esters >
Homoenolates are generated by reaction of N-heterocycle carbenes with enals, leading to carbon-carbon bond formation or activated carboxylates depending on the used base. The design of a new triazolium precatalyst enabled the catalytic, atom-economical redox esterification of enals.
S. S. Sohn, J. W. Bode, Org. Lett., 2005, 7, 3873-3876.
N-Heterocyclic carbenes are effective catalysts for an Umpolung reaction of α,β-unsaturated aldehydes. The generated homoenolate species can be protonated, and the resulting activated carbonyl unit is trapped with an alcohol nucleophile to form a saturated ester.
A. Chan, K. A. Scheidt, Org. Lett., 2005, 7, 905-908.
A cooperative catalyst system enhances both yield and selectivity of an enantioselective N-heterocyclic carbene (NHC)-catalyzed β-protonation providing a broad range of aryl-oxobutenoates and highly enantioenriched succinate derivatives. The method demonstrates the benefits of combining different activation modes in organocatalysis.
M. H. Wang, D. T. Cohen, C. Benjamin Schwamb, R. K. Mishra, K. A. Scheidt, J. Am. Chem. Soc., 2015, 137, 5891-5894.
A readily prepared, inexpensive thiolate-based catalyst enables a highly selective, atom-economical crossed Tishchenko disproportionation of ortho-substituted benzaldehydes with other aromatic aldehydes. The methodology is of exceptionally wide scope and exhibits a high functional-group tolerance.
S. P. Curran, S. J. Connon, Angew. Chem. Int. Ed., 2012, 51, 10866-10870.
For Tishchenko reactions, selenide ions are superior catalysts to previously reported thiolate analogues. These catalysts promote the disproportionation of aldehydes with increased reaction rates and broader scope at lower catalyst loadings and temperatures. Significantly improved catalyst performance was also observed in the aryl selenide mediated crossed intermolecular Tishchenko reaction.
S. P. Curran, S. J. Connon, Org. Lett., 2012, 14, 1074-1077.
The catalytic generation of activated carboxylates from epoxyaldehydes enables a direct, anti-selective, convenient and mild synthesis of β-hydroxyesters.
K. Y.-K. Chow, J. W. Bode, J. Am. Chem. Soc., 2004, 126, 8126-8127.