Categories: C=O Bond Formation >
Synthesis of esters
N-Heterocyclic carbenes catalyze the oxidation of various allylic, propargylic, and benzylic alcohols to esters with manganese(IV) oxide in excellent yields. Saturated esters can also be accessed from aldehydes using this method. A desymmetration of meso-1,2-diols using a chiral catalyst is described.
B. E. Maki, A. Chan, E. M. Phillips, K. A. Scheidt, Org. Lett., 2007, 9, 371-374.
Screening of simple binary and ternary admixtures of Pd/charcoal in combination with one or two metal and/or metalloid components as the catalyst for aerobic oxidative methyl esterification of primary alcohols revealed two very effective catalyst compositions. One was used in batch aerobic oxidation reactions, whereas the other achieved nearly 60 000 turnovers in a continuous-flow packed-bed reactor with no apparent loss of catalytic activity.
D. S. Mannel, M. S. Ahmed, T. W. Root, S. S. Stahl, J. Am. Chem. Soc., 2017, 139, 1690-1698.
A readily accessible catalyst system consisting of Pd/charcoal in combination with bismuth(III) nitrate and tellurium metal enables an efficient aerobic oxidative methyl esterification of primary alcohols, exhibits a broad substrate scope, and is effective with both activated and unactivated alcohols bearing diverse functional groups. The Bi and Te additives significantly increase the reaction rate, selectivity, and overall product yields.
A. B. Powell, S. S. Stahl, Org. Lett., 2013, 15, 5072-5075.
Oxidative methyl esterification of primary alcohols and diols with methanol in the presence of acetone as a hydrogen acceptor was successfully achieved under catalysis of an iridium complex combined with 2-(methylamino)ethanol (MAE).
N. Yamamoto, Y. Obora, Y. Ishii, J. Org. Chem., 2011, 76, 2937-2941.
A highly effective synthesis of methyl esters from benzylic alcohols, aldehydes, or acids via copper-catalyzed C-C cleavage from tert-butyl hydroperoxide is easily accessible and practical and offers an alternative to the traditional way.
Y. Zhu, H. Yan, L. Lu, D. Liu, G. Rong, J. Mao, J. Org. Chem., 2013, 78, 9898-9905.
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.
Alcohols and aldehydes can be oxidized to the corresponding methyl esters by reaction with methanol in the presence of crotononitrile as a hydrogen acceptor using a catalyst combination of Ru(PPh3)3(CO)H2 with xantphos.
N. A. Owston, T. D. Nixon, A. J. Parker, M. K. Whittlesey, J. M. J. Williams, Synthesis, 2009, 1459-1462.
A metal-free esterification of a broad range of alkynes with alcohols in the presence of phenyliodine bis(trifluoroacetate) produces esters in good yields via carbon triple bond cleavage. The transformation proceeds via hydroxyethanones and ethanediones as intermediates and exhibits a broad substrate scope and good functional group tolerance.
Q. Jiang, A. Zhao, B. Xu, J. Jia, X. Liu, C. Guo, J. Org. Chem., 2014, 79, 2709-2715.
Cobalt bis(acetylacetonate) mediates hydrogen atom transfer to a broad range of functionalized alkenes. In situ oxidation of the resulting alkylradical intermediates, followed by hydrolysis, provides expedient access to ketones and esters. This method is compatible with a number of functional groups and provides a mild and practical alternative to the Tamao-Fleming oxidation of vinylsilanes and the Arndt-Eistert homologation.
X. Ma, S. B. Herzon, J. Org. Chem., 2016, 81, 8673-8695.
An efficient oxidation of various acetals, including open-chain acetals, 1,3-dioxanes and 1,3-dioxalanes, with molecular oxygen in the presence of catalytic amounts of N-hydroxyphthalimide (NHPI) and Co(OAc)2 as co-catalyst gave esters.
B. Karimi, J. Rajabi, Synthesis, 2003, 2373-2377.
In the presence of hydrogen peroxide and trimethylsilyl chloride, thiocarbonyls desulfurize to the corresponding carbonyls in short reaction times with no side reactions and excellent selectivity. This process is a safe, operationally simple, and environmentally benign alternative for the desulfurization of thiocarbonyls.
K. Bahrami, M. M. Khodaei, M. Tajik, Synthesis, 2010, 4282-4286.
The oxidation of malononitrile derivatives with peracid in methanol proceeds with loss of the cyano groups to yield methyl esters in high yield. The method was applied to a variety of malononitrile derivatives, some of which were prepared by Pd- or Ir-catalyzed asymmetric allylic substitution.
S. Förster, O. Tverskoy, G. Helmchen, Synlett, 2008, 2803-2806.
Cu/nitroxyl catalysts promote a highly efficient and selective aerobic oxidative lactonization of diols under mild reaction conditions using ambient air as the oxidant. A Cu/ABNO catalyst system shows excellent reactivity with symmetrical diols and hindered unsymmetrical diols, whereas a Cu/TEMPO catalyst system displays excellent chemo- and regioselectivity for the oxidation of less hindered unsymmetrical diols.
X. Xie, S. S. Stahl, J. Am. Chem. Soc., 2015, 137, 3767-3770.
In the presence of TBAI/TBHP, treatment of esters possessing a methylene carbon α-to oxygen with benzylamines provides bis-esters rather than the expected amides. Under these oxidative conditions, benzylamines generate less nucleophilic carboxylates, which couple at sp3 C-H bonds of esters and cyclic ethers to yield bis-acyl ketals and α-acyloxy ethers, respectively.
G. Majji, S. Rajamanickam, N. Khatun, S. K. Santra, B. K. Patel, J. Org. Chem., 2015, 80, 3440-3446.