Synthesis of amides by rearrangements, hydrolysis, or oxidation
A modular Cu/ABNO catalyst system enables efficient aerobic oxidative coupling of alcohols and amines to amides. All four permutations of benzylic/aliphatic alcohols and primary/secondary amines are viable in this reaction, enabling broad access to secondary and tertiary amides with excellent functional group compatibility within short reaction time at rt.
S. L. Zultanski, J. Zhao, S. S. Stahl, J. Am. Chem. Soc., 2016, 138, 6416-6419.
A Cu2O-catalyzed aerobic oxidative decarboxylative ammoxidation of phenylacetic acids and α-hydroxyphenylacetic acids enables the synthesis of various primary benzamides in good yields. This one-pot domino protocol combines decarboxylation, dioxygen activation, oxidative C-H bond functionalization, and amidation reactions.
Q. Song, Q. Feng, K. Yang, Org. Lett., 2014, 16, 624-627.
A simple ruthenium catalyst mediates a direct coupling between an alcohol and an amine with the liberation of two molecules of dihydrogen. The active catalyst is generated in situ from an easily available ruthenium complex, an N-heterocyclic carbene and a phosphine. The reaction allows primary alcohols to be coupled with primary alkylamines to afford secondary amides in good yields.
L. U. Nordstrřm, H. Vogt, R. Madsen, J. Am. Chem. Soc., 2008, 130, 17672-17673.
An in situ generated catalyst from readily available RuH2(PPh3)4, an N-heterocyclic carbene (NHC) precursor, NaH, and acetonitrile showed high activity for the amide synthesis directly from either alcohols or aldehydes with amines.
S. Muthaiah, S. C. Ghosh, J.-E. Jee, C. Chen, J. Zahng, S. H. Hong, J. Org. Chem., 2010, 75, 3002-3006.
Hypervalent iodine reagents promote a facile and efficient transformation of primary amides to secondary amides. The hypervalent iodine reagent mediates a Hofmann-type rearrangement to an isocyanate intermediate, which is subsequently trapped by an in situ generated carboxylic acid from the hypervalent iodine reagent to provide the corresponding secondary amides.
X. Wang, P. Yang, B. Hu, Q. Zhang, D. Li, J. Org. Chem., 2021, 86, 2820-2826.
In a completely atom-economical and redox-neutral catalytic amide synthesis from an alcohol and a nitrile, the amide C–N bond is efficiently formed between the nitrogen atom of nitrile and the α-carbon of alcohol, with the help of an N-heterocyclic carbene-based ruthenium catalyst, without a single byproduct.
B. Kang, Z. Fu, S. H. Hong, J. Am. Chem. Soc., 2013, 135, 11704-11707.
An efficient, metal-free domino protocol for the synthesis of benzamides from ethylarenes proceeds through the formation of triiodomethyl ketone intermediate in the presence of iodine as the promoter and TBHP as an oxidant followed by nucleophilic substitution with aqueous ammonia. This operationally simple, functional-group-tolerant tandem approach provides an easy access to the broad range of biologically important benzamides.
K. S. Vadagaonkar, H. P. Kalmode, S. Prakash, A. C. Chaskar, Synlett, 2015, 26, 1677-1682.
CpRuCl(PPh3)2 catalyzes reactions of terminal alkynes with primary and secondary amines to afford the corresponding amides in the presence of 4-picoline N-oxide. The reactions occur in chlorinated solvent and aqueous medium, showing applications in peptide chemistry.
A. Álvarez-Pérez, M. A. Esteruelas, S. Izquierdo, J. A. Varela, C. Saá, Org. Lett., 2019, 21, 5346-5350.
In an unusual oxidative coupling reaction of isocyanide and toluene derivatives using tetrabutylammonium iodide (TBAI) as a catalyst, the isocyano group acts formally as an N1 synthon, thus expanding the reactivity profile of isocyanides.
Z. Liu, X. Zhang, J. Li, F. Li, C. Li, X. Jia, J. Li, Org. Lett., 2016, 18, 4032-4035.
A facile copper-catalyzed ipso-amidation of arylboronic acids with nitriles enables a highly efficient and economical synthesis of N-aryl amides with a broad substrate scope.
Y. Qiao, G. Li, S. Liu, Y. Yangkai, J. Tu, F. Xu, Synthesis, 2017, 49, 1834-1838.
The use of tert-butyl hydroperoxide as an oxidant and an inexpensive and air stable copper catalyst enables a simple and efficient protocol for the oxidative amidation of commercially affordable alcohols to Weinreb amides in very good yields. The reaction tolerates various functional groups.
S. L. Yedage, B. M. Bhanage, Synthesis, 2015, 47, 526-532.
A dimethyl sulfoxide (DMSO)-promoted oxidative amidation reaction between 2-oxoaldehydes and amines under metal-free conditions enables an efficient synthesis of α-ketoamides. Mechanistic studies supported an iminium ion intermediate that reacts with DMSO to provide the C1-oxygen atom of the product.
N. Mupparapu, S. Khan, S. Battula, M. Kushwaha, A. P. Gupta, Q. N. Ahmed, R. A. Vishwakarma, Org. Lett., 2014, 16, 1152-1155.
A Cu-catalyzed oxidative amidation-diketonization reaction of terminal alkynes leads to α-ketoamides. In this copper-catalyzed radical process, O2 not only participates as the ideal oxidant but also undergoes dioxygen activation under ambient conditions.
C. Zhang, N. Jiao, J. Am. Chem. Soc., 2010, 132, 28-29.
A copper-catalyzed one-pot strategy for the synthesis of α-ketoamides from 1-arylethanols is highly efficient and delivers product in very good yields via alcohol oxidation, sp3 C-H oxidation, and oxidative amidation.
N. Sharma, S. S. Kotha, N. Lahiri, G. Sekar, Synthesis, 2015, 47, 726-736.
The combination of zinc powder as reductant and sodium chlorate as oxidant was used to provide an environmentally friendly, effective, and convenient method for the synthesis of aromatic amides in good yields from nitroarenes and aldehydes in a green solvent under atmospheric conditions. Reductants and oxidants with opposing properties can be used together without any adverse effects. In addition, a cooperation seems to improve the yield.
G. Sheng, X. Wu, X. Cai, W. Zhang, Synthesis, 2015, 47, 949-954.
A wide range of aldoximes has been converted into the corresponding amides in high yield and selectivity using the ruthenium-based catalyst Ru(PPh3)3(CO)H2/dppe/TsOH with catalyst loading as low as 0.04 mol%.
N. A. Owston, A. J. Parker, J. M. J. Williams, Org. Lett., 2007, 9, 3599-3601.
[Ir(Cp*)Cl2]2 catalyzes the rearrangement of oximes to furnish amides. An iridium-catalyzed transfer hydrogenation between alcohols and styrene and the subsequent formation of an oxime allows the conversion of alcohols into amides in a one-pot process.
N. A. Owston, A. J. Parker, J. M. J. Williams, Org. Lett., 2007, 9, 73-75.
A one-carbon homologation of an alcohol to the extended carboxylic acid, ester, or amide involves a Mitsunobu reaction with an alkoxymalononitrile, followed by unmasking in the presence of a suitable nucleophile. The homologation and unmasking can even be performed in a one-pot process in high yield.
N. Kagawa, A. E. Nibbs, V. H. Rawal, Org. Lett., 2016, 18, 2363-2366.