A one-pot conversion of aldehydes to esters interfaces N-heterocyclic carbene-based organocatalysis with electro-organic synthesis to achieve direct oxidation of catalytically generated electroactive intermediates. A broad range of aldehyde and alcohol substrates has been converted. Furthermore, the anodic oxidation reactions are very clean, producing only H2 gas as a result of cathodic reduction.
E. E. Finney, K. A. Ogawa, A. J. Boydston, J. Am. Chem. Soc., 2012, 134, 12374-12377.
N-Heterocyclic carbenes catalyze the oxidation of unactivated aldehydes to esters with manganese(IV) oxide in excellent yield under mild conditions. The reaction proceeds through a transient activated alcohol generated in situ and preserves stereochemical integrity. Various esters can be synthesized using a broad range of alcohols and unactivated aldehydes.
B. E. Marki, K. A. Scheidt, Org. Lett., 2008, 10, 4331-4334.
VO(acac)2 catalyzes the oxidation of aromatic and aliphatic aldehydes to the corresponding acids efficiently and selectively in the presence of hydrogen peroxide as an oxidant. This method offers functional-group compatibility, easy workup procedure, and a short reaction time. The performance of titania-supported VO(acac)2 in the oxidation of aldehydes was also investigated.
D. Talukdar, K. Sharma, S. K. Bharadwaj, A. J. Thakur, Synlett, 2013, 24, 963-966.
An efficient N-heterocyclic carbene (NHC)-mediated oxidative esterification of aldehydes in an undivided microfluidic electrolysis cell provides up to 4.3 g h-1 of product in a single pass with excellent yields at ambient temperature. The oxidative acylation reactions proceed with a 1:1 stoichiometry of aldehyde and alcohol (for primary alcohols) with remarkably short residence times in the electrolysis cell (<13 s) without electrolyte.
R. A. Green, D. Pletcher, S. G. Leach, R. C. D. Brown, Org. Lett., 2015, 17, 3290-3293.
A simple, efficient, and high-yield procedure for the oxidative conversion of alcohols to various types of esters and ketones was successfully carried out with molecular iodine as the oxidant and potassium carbonate.
N. Mori, H. Togo, Tetrahedron, 2005, 61, 5915-5925.
Highly efficient, mild, and simple protocols allow the oxidation of aldehydes to carboxylic acids and esters utilizing Oxone as the sole oxidant. These reactions may prove to be valuable alternatives to traditional metal-mediated oxidations.
B. R. Travis, M. Sivakumar, G. O. Hollist, B. Borhan, Org. Lett., 2003, 5, 1031-1034.
In a mild and efficient oxidative esterification using TCCA as the oxidant, aromatic and aliphatic aldehydes are converted in situ into their corresponding acyl chlorides, which are then reacted with primary and secondary aliphatic, benzylic, allylic, and propargylic alcohols and phenols to give various esters in high yields.
S. Gaspa, A. Porcheddu, L. De Luca, Org. Lett., 2015, 17, 3666-3669.
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.
Cooperative carbene catalysis allows selective oxidative acylations of alcohols with aldehydes even in the presence of amino groups by using a readily available cheap organic oxidant. Quantum chemical calculations support the suggested mechanism.
S. De Sarkar, S. Grimme, A. Studer, J. Am. Chem. Soc., 2010, 132, 1190-1191.
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.
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.
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.
Aldehydes and siloxanes form methyl esters in a single step through mild oxidative esterification in the presence of a palladium catalyst or, alternatively, afford secondary alcohols via TBAF-promoted arylation in the absence of a catalyst at increased temperatures.
R. Lerebours, C. Wolf, J. Am. Chem. Soc., 2006, 128, 13052-13053.
Aldehydes undergo oxidative transformation to the methyl esters in methanol as solvent upon treatment with catalytic amounts of vanadium pentoxide in combination with hydrogen peroxide. This method features mild reaction conditions, short reaction times, high efficiencies, cost-effectiveness, and facile isolation of the desired products.
R. Gopinath, B. Patel, Org. Lett., 2000, 2, 577-579.
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.
Copper(II) catalyzes a cross dehydrogenative coupling (CDC) reaction of aldehydes with alkylbenzenes in the presence of TBHP to yield benzylic esters.
S. K. Rout, S. Guin, K. K. Ghara, A. Banerjee, B. K. Patel, Org. Lett., 2012, 14, 3982-3985.
Copper-catalyzed aerobic oxidative esterification of acetophenones with alcohols using molecular oxygen gives a broad range of α-ketoesters in good yields. Mechanism studies evealed that the carbonyl oxygen in the ester mainly originated from dioxygen.
X. Xu, W. Ding, Y. Lin, Q. Song, Org. Lett., 2015, 17, 516-519.
An enantioselective synthesis of γ-nitroesters by a one-pot asymmetric Michael addition/oxidative esterification of α,β-unsaturated aldehydes is based on an enantioselective organocatalytic nitroalkane addition followed by an N-bromosuccinimide-based oxidation. The γ-nitroesters are obtained in good yields and enantioselectivities, and the method provides an attractive entry to optically active γ-aminoesters, 2-piperidones, and 2-pyrrolidones.
K. L. Jensen, P. H. Poulsen, B. S. Donslund, F. Morana, K. A. Jørgensen, Org. Lett., 2012, 14, 1516-1519.