Categories: C-O Bond Formation >
Synthesis of esters
Dimethylcarbonate is a nontoxic and green methylating reagent. A base-catalyzed methyl transfer from dimethylcarbonate to carboxylic acids offers high selectivity for esterification and mild reaction conditions, that enable conservation of stereochemistry at epimerizable stereocenters. Isotope-labeling studies suggest a mechanism via direct methyl transfer from dimethylcarbonate to the substrate.
Y. Ji, J. Sweeney, J. Zoglio, D. J. Gorin, J. Org. Chem., 2013, 78, 11606-11611.
A Cu-catalyzed nondecarboxylative methylation of carboxylic acids with methylboronic acid proceeds in air as sole oxidant and offers a strategy for replacing toxic, electrophilic alkylating reagents. An isotope-labeling study supports an oxidative cross-coupling mechanism, in analogy to that proposed for Chan-Lam arylation.
C. E. Jacobson, N. Martinez-Mu˝oz, D. J. Gorin, J. Org. Chem., 2015, 80, 7305-7310.
A copper-catalyzed O-methylation of carboxylic acids using dimethyl sulfoxide (DMSO) as the methyl source exhibits a broad substrate scope and excellent functional group tolerance. Mechanistic studies indicate that a methyl radical is generated from dimethyl sulfoxide.
J. Jia, Q. Jiang, A. Zhao, B. Xu, Q. Liu, W.-P. Luo, C.-C. Guo, Synthesis, 2016, 48, 421-428.
Methyl salicylate is a selective and inexpensive methylating agent for the esterification of carboxylic acids with a wide range of functional group tolerance. The intramolecular hydrogen bonds between the carboxylate and hydroxyl groups in methyl salicylate are essential for the transformation. Allyl, benzyl, methallyl, and propargyl salicylates can also be used as alkylating agents for the preparation of the corresponding alkyl carboxylates.
S. Chen, L. Jia, X. Li, M. Luo, Synthesis, 2014, 46, 263-268.
A very fast, microwave-assisted formation of carboxylic esters via reaction of carboxylic acids with O-alkylisoureas derived from primary and secondary alcohols proceeds in good yields with clean inversion of configuration where appropriate. The reaction works well with very hindered carboxylic acids.
A. Chighine, S. Crosignani, M.-C. Arnal, M. Bradley, B. Linclau, J. Org. Chem., 2009, 74, 4638-4641.
Treatment of methylarenes with 1,3-dibromo-5,5-dimethylhydantoin or N-bromosuccinimide and a catalytic amount of 2,2′-azobis(isobutyronitrile) followed by a reaction with a nucleophile, such as benzoic acid, p-toluenethiol, sodium p-toluenesulfinate, aqueous dimethylamine, or succinimide, provides the corresponding benzylated products in good yields.
H. Shimojo, K. Moriyama, H. Togo, Synthesis, 2015, 47, 1280-1290.
Nucleophilic fluorination using CsF or alkali metal fluorides was completed in short reaction time in the presence of [bmim][BF4] affording the desired products without any byproducts. Facile nucleophilic substitutions such as halogenations, acetoxylation, nitrilation, and alkoxylations in the presence of ionic liquids provided the desired products in good yields.
D. W. Kim, C. E. Song, D. Y. Chi, J. Org. Chem., 2003, 68, 4281-4285.
Ionic liquids [bmim][X] (X = Cl, Br, I, OAc, SCN) are highly efficient reagents for nucleophilic substitution reactions of sulfonate esters derived from primary and secondary alcohols. The newly developed protocol is very environmentally attractive because the reactions use stoichiometric amounts of ionic liquids as sole reagents without additional solvents and activating reagents. Moreover, these ionic liquids can be readily recycled.
Y. Liu, Y. Xu, S. H. Jung, J. Chae, Synlett, 2012, 23, 2663-2666.
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.
An efficient arylation of carboxylic acids with diaryliodonium salts gives aryl esters in high yields within short reaction times for both aromatic and aliphatic substrates. The transition-metal-free conditions are compatible with a range of functional groups, and good chemoselectivity is observed with unsymmetric diaryliodonium salts. Furthermore, steric hindrance in the ortho positions is well tolerated.
T. B. Petersen, R. Khan, B. Olofsson, Org. Lett., 2011, 13, 3454-3457.
A direct catalytic anti-Markovnikov addition of carboxylic acids to alkenes is comprised of the Fukuzumi acridinium photooxidant and a substoichiometric quantity of a hydrogen-atom donor. Oxidizable olefins, such as styrenes, trisubstituted aliphatic alkenes, and enamides, can be employed along with a variety of carboxylic acids to afford the anti-Markovnikov addition adducts exclusively.
A. J. Perkowski, D. A. Nicewicz, J. Am. Chem. Soc., 2013, 135, 10334-10337.
An efficient two-step protocol that employs readily available terminal alkenes as starting materials enables a highly regio- and stereoselective synthesis of various allylic acetates. This method affords linear (E)-isomers and tolerates several functional groups including halogen-containing molecules. For other weak oxygen, carbon, nitrogen, and sulfur nucleophiles, adducts were obtained in very good yields too.
X. Huang, B. Fulton, K. White, A. Bugarin, Org. Lett., 2015, 17, 2594-2597.
The presence of a base strongly improves the efficiency and the selectivity of the Pd-catalyzed oxidation of terminal alkenes in carboxylic acids. The methodology is particularly well adapted for the oxidation of homoallylic alcohols, for which the resulting acyloxylated products are obtained selectively as E-isomers in good yields.
E. Thiery, C. Aouf, J. Belloy, D. Harakat, J. Le Bras, J. Muzart, J. Org. Chem., 2010, 75, 1771-1774.
An oxidative decarboxylation of β,γ-unsaturated carboxylic acids mediated by PhI(OAc)2 gives the corresponding allylic acetates. In addition, a decarboxylative C-N bond formation was achieved. Mechanistic studies suggest an unique reactivity of hypervalent iodine reagents in this ionic oxidative decarboxylation.
K. Kiyokawa, S. Yahata, T. Kojima, S. Minakata, Org. Lett., 2014, 16, 4646-4649.
A method for the preparation of a wide range of branched allylic esters from terminal alkynes proceeds via a redox-neutral propargylic CH activation employing a rhodium(I)/DPEphos catalyst.
A. Lumbroso, P. Koschker, N. R. Vautravers, B. Breit, J. Am. Chem. Soc., 2011, 133, 2386-2389.
A rhodium-catalyzed N-H and O-H insertion of amides and carboxylic acids with α-diazo-β-ketoesters gives different α-amido- and α-carboxylic-β-ketoesters in good yields. The reactions were performed under mild conditions with 1 mol% of catalyst.
S. Bertelsen, M. Nielsen, S. Bachmann, K. A. Jorgensen, Synthesis, 2005, 2234-2238.
"Activated" dimethyl sulfoxide efficiently dehydrogenates hydrazones to the respective diazo compounds at -78░C. Under optimized conditions, simple vacuum filtration provides solutions of pure diazo compounds from which stable diazo species can be isolated in high yield, or that can be directly used in subsequent reactions.
M. I. Javed, M. Brewer, Org. Lett., 2007, 9, 1789-1792.
0.01 mol-% Zinc(II) salts catalyze the reaction between acetals and acid halides to provide haloalkyl ethers in near-quantitative yield in 1 - 4 h. The solutions of haloalkyl ethers can be utilized directly in reactions in which the presence of the ester byproduct does not interfere. Excess carcinogenic haloalkyl ether is destroyed on workup.
M. A. Berliner, K. Belecki, J. Org. Chem., 2005, 70, 9618-9621.
A Cu(OTf)2-mediated Chan-Lam reaction of carboxylic acids with arylboronic acids is a facile and practical methodology to access phenolic esters in good yields. The procedure tolerates various functional groups, such as methoxycarbonyl, acetoxy, free phenolic hydroxyl, vinyl, nitro, trifluoromethyl, methoxyl, bromo, chloro, iodo, and acetyl groups.
L. Zhang, G. Zhang, M. Zhang, J. Cheng, J. Org. Chem., 2010, 75, 7472-7474.
An efficient, mild and transition-metal-free N-arylation of amines, sulfonamides, and carbamates and O-arylation of phenols and carboxylic acids has been achieved by using various o-silylaryl triflates in the presence of CsF.
Z. Liu, R. C. Larock, J. Org. Chem., 2006, 71, 3198-3209.
Various anilides have been directly ortho-acetoxylated with acetic acid as the acetate source and K2S2O8 as the oxidant in the presence of Pd(OAc)2 as catalyst. The amide group is an elegant directing group to convert aromatic sp2 C-H bonds into C-O bonds.
G.-W. Wang, T.-T. Yuan, X.-L. Wu, J. Org. Chem., 2008, 73, 4717-4720.
A mild copper-catalyzed Chan-Lam-Evans type cross-coupling reaction enables a stereospecific and regioselective preparation of enol esters from carboxylate salts or carboxylic acids and potassium alkenyltrifluoroborate salts in the presence of oxygen, catalytic CuBr, DMAP and 4 ┼ molecular sieves. Overall, this method demonstrates carboxylic acids as suitable reaction partners for nondecarboxylative copper-catalyzed cross-couplings.
F. Huang, T. D. Quach, R. A. Batey, Org. Lett., 2013, 15, 3058-3061.
A rhodium-catalyzed, selective intermolecular anti-Markovnikov addition of carboxylic acids to terminal alkynes gives valuable Z-enol esters. The catalyst system is applicable to a broad substrate scope and displays a wide functional group tolerance.
A. Lumbroso, N. R. Vautravers, B. Breit, Org. Lett., 2010, 12, 5498-5501.
Ruthenium complexes were successfully applied in highly regioselective Markovnikov additions of carboxylic acids to terminal alkynes, yielding valuable enol esters. Selectivity and activity could be further improved by the addition of catalytic amounts of AgOTf. A broad range of simple as well as electronically or sterically challenging substrates could be isolated in good to excellent yields with high regioselectivity and under mild reaction conditions.
J. Jeschke, C. Gńbler, H. Lang, J. Org. Chem., 2016, 81, 476-484.
PPh3AuCl/AgPF6-catalyzed hydroacyloxylation of alkynes with carboxylic acids affords the Markonikov addition products, whereas PPh3AuCl/AgOTf catalyst gives the more stable isomerized products via the Markonikov products.
B. C. Chary, S. Kim, J. Org. Chem., 2010, 75, 7928-7931.
A gold(I)-catalyzed rearrangement of diversely substituted allenyl carbinol esters allows the efficient, rapid, and stereoselective synthesis of various functionalized 1,3-butadien-2-ol esters via a new 1,3-shift of an ester moiety onto a gold-activated allene.
A. K. Buzas, F. M. Istrate, F. Gagosz, Org. Lett., 2007, 9, 985-988.
The preparation of diverse β-chloroethers, β-chloroacetates, and chlorohydrins is efficiently achieved under mild conditions by reaction of alkenes with trichloroisocyanuric acid in alcohols, acetic acid or aqueous acetone, respectively.
G. Fonseca Mendonša, A. Manzolillo Sanseverino, M. C. S. de Mattos, Synthesis, 2003, 45-48.
A new palladium-catalyzed method allows the oxygenation of unactivated sp3 C-H bonds of a wide variety of alkane substrates containing readily available oxime and/or pyridine directing groups with extremely high levels of chemo-, regio-, and in some cases diastereoselectivity.
L. V. Desai, K. L . Hull, M. S. Sanford, J. Am. Chem. Soc., 2004, 126, 9542-9543.