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Synthesis of amides
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An effective protocol for a waste-minimized, environmentally benign thermal
condensation of carboxylic acids with amines has been identified. Fourteen
examples demonstrate the applicability of this procedure to aliphatic, aromatic
and heteroaromatic carboxylic acids and primary and secondary aliphatic as well
as aromatic amines. The approach leads to the corresponding amides in good
yields.
L. J. Gooßen, D. M. Ohlmann, P. P. Lange, Synthesis, 2009,
160-164.

Nanosized sulfated titania was prepared by a sol-gel hydrothermal process. The
nanoparticles showed high catalytic activity in a direct amidation of fatty
acids as well as benzoic acids with various amines under solvent-free conditions.
M. Hosseini-Sarvari, E. Sodagar, M. M. Doroodmand, J. Org. Chem., 2011,
76, 2853-2859.

Borane-tetrahydrofuran complex or borane-methyl sulfide complex is used to
generate triacyloxyboranes, which can be effectively reacted with various
nucleophiles (alkylamines, arylamines, hydrazides, alcohols, phenols) at reflux
in toluene to provide the corresponding amides and esters in excellent yield.
Z. Huang, J. R. Reilly, R. N. Buckle, Synlett, 2007,
1026-1030.

The conversion of carboxylic acids to their corresponding acid chlorides occurs
rapidly in the presence a tertiary amine base and 3,3-dichlorocyclopropenes via
aromatic cation-activated nucleophilic acyl substitution. The effect of
cyclopropene substituents on the rate of conversion is examined. Conditions were
developed for the preparation of acid sensitive acid chlorides.
D. J. Hardee, L. Kovalchuke, T. H. Lambert, J. Am. Chem. Soc., 2010,
132, 5002-5003.

The use of magnesium nitride as a convenient source of ammonia allows a direct
transformation of esters to primary amides. Methyl, ethyl, isopropyl, and
tert-butyl esters are converted to the corresponding carboxamides in
good yields.
G. E. Veitch, K. L. Bridgwood, S. V. Ley, Org. Lett.,
2008,
10, 3623-3625.

An iodine-NH3 • H2O system enables a direct transformation
of aryl, heteroaryl, vinyl, or ethynyl methyl ketones or carbinols to the
corresponding primary amides in good yields in aqueous media. A tandem
Lieben-Haller-Bauer reaction mechanism is proposed.
L. Cao, J. Ding, M. Gao, Z. Wang, J. Li, A. Wu, Org. Lett., 2009,
11, 3810-3813.

The use of PhI=NTs/PhI=NNs as the nitrogen source in the presence of inexpensive iron(II) chloride + pyridine
as the in situ formed precatalyst enables amidation of aldehydes under mild conditions at room temperature or microwave assisted conditions.
The protocol is operationally straightforward and accomplished in good product yields and with complete chemoselectivity.
T. M. U. Ton, C. Tejo, S. Tania, J. W. W. Chang, P. W. H. Chan, J. Org. Chem., 2011,
76, 4894-4904.

N-Cbz-protected amino acids reacted with various aryl amines in the
presence of methanesulfonyl chloride and N-methylimidazole in
dichloromethane to give the corresponding arylamides in high yields without
racemization under these mild conditions.
L. Mao, Z. Wang, Y. Li, X. Han, W. Zhou, Synlett, 2011,
129-133.

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) catalyzes the amidation of acyl
imidazoles. The rate acceleration is especially evident with traditionally
unreactive, electron-deficient anilines. DBU offers safety and cost advantages
over more commonly employed catalysts such as 1-hydroxybenzotriazole (HOBt).
C. Larrive-Aboussafy, B. P. Jones, K. E. Price, M. A. Hardink, R. W. McLaughlin,
B. M. Lillie, J. M. Hawkins, R. Vaidyanathan, Org. Lett., 2010,
12, 324-327.

Malonic acid derivatives undergo unusually mild decarboxylation in the
presence of N,N′-carbonyldiimidazole (CDI) at room temperature to
generate a carbonyl imidazole intermediate in high yield. Subsequent reactions with
various nucleophiles in an efficient one-pot process leads to amides, esters or carboxylic acids.
D. Lafrance, P. Bowles, K. Leeman, R. Rafka, Org. Lett., 2011,
13, 2322-2325.

Deprotonated 1,2,4-triazole is an active acyl transfer catalyst suitable for
the aminolysis and transesterification of esters.
X. Yang, V. B. Birman, Org. Lett., 2009,
11, 1499-1502.

A N-heterocyclic carbene catalyzes the oxidative esterification of various
aldehydes in the presence of 3,3',5'5-tetra-tert-butyldiphenoquinone to
yield hexafluoroisopropylesters, which are useful active esters for in situ
amide bond formation. This transition metal-free organocatalytic system also
enabled a mild oxidative azidation of aldehydes.
S. De Sarkar, A. Studer, Org. Lett., 2010,
12, 1992-1995.

Amines are efficiently acylated
by both cyclic and acyclic anhydrides in aqueous medium with sodium dodecyl
sulfate (SDS) - without use of acidic or basic reagents. Various amines and
anhydrides were reacted with equal ease. Chemoselective acylation in the
presence of phenols and thiols has been achieved. No chromatographic
separation is required for isolation of the acylated products.
S. Naik, G. Bhattacharjya, B. Talukdar, B. K. Patel,
Eur. J. Org. Chem., 2004, 1254-1260.

Various alcohols, thiols, phenols, and amines can be acetylated using acetic
anhydride in the presence of catalytic quantity of silver triflate. The method
proceeds under mild conditions, does not involve cumbersome workup, and the
resulting products are obtained in high yields within a reasonable time.
R. Das, D. Chakraborty, Synthesis, 2011,
1621-1625.

Phosphomolybdic acid (PMA) is a simple and efficient catalyst for the
acetylation of structurally diverse alcohols, phenols, and amines. Acetylation
reactions with acetic anhydride proceed in excellent yield in the presence of a
catalytic amount of PMA at ambient temperature within a relatively short
reaction time under solvent-free conditions.
S. T. Kadam, S. S. Kim, Synthesis, 2008,
267-268.

Copper(II) tetrafluoroborate efficiently catalyzes acetylation of
structurally diverse phenols, alcohols, thiols, and amines with
stoichiometric amounts of Ac2O under solvent-free conditions at
room temperature. Acid-sensitive alcohols are smoothly acetylated without
competitive side reactions.
A. K. Chakraborti, R. Gulhane, Shivani, Synthesis, 2004,
111-115.

Multivalent metal salts, such as ferric chloride and sulfate, are active and
versatile catalysts for the amidation of aliphatic fatty acids with long-chain
aliphatic amines.
Y. Terada, N. Ieda, K. Komura, Y. Sugi, Synthesis, 2008,
2318-2319.

Aliphatic, aromatic, and heteroaromatic carboxylic acids in the form of their
salts condense with aryl isocyanates at room temperature with loss of carbon
dioxide to give the corresponding amides in high yield. Application of the
reaction to acyl isocyanates gives unsymmetric imides. The reaction is
compatible with hydroxyl groups and both Fmoc and Boc protecting groups for
amines.
K. Sasaki, D. Crich, Org. Lett., 2011,
13, 2256-2259.

2,2′-Dipyridyl diselenide catalyzes a direct reaction of carboxylic acids with
azides and trimethylphosphine at room temperature. The mechanism of the process,
which is not an aza-Wittig reaction, has been elucidated.
J. Burés, M. Martín, F. Urpí, J. Vilarrasa, J. Org. Chem., 2009,
74, 2203-2206.

2-Acyl-4,5-dichloropyridazin-3-ones served as stable, convenient and
chemoselective N-acylating reagents for amines under neutral
conditions.
Y.-J. Kang, H.-A Chung, J.-J. Kim, Y.-J. Yoon, Synthesis,
2002, 733-738.

The reaction of N,N-dialkylformamide dimethyl acetal with primary amides
produces N'-acyl-N,N-dialkylformamidines as intermediates. In the
presence of certain Lewis acid additives efficient acyl transfer occurs,
providing new and useful methods for amide exchange such as transamidation.
T. A. Dineen, M. A. Zajac, A. G. Myers, J. Am. Chem. Soc., 2006,
128, 16406-16409.

A novel amide bond formation strategy from simple thioacid and amine starting
materials is mediated by unstable but very reactive S-nitrosothioacid
intermediates. This fast reaction under mild conditions should be useful in
synthesis.
J. Pan, N. O. Devarie-Baez, M. Xian, Org. Lett., 2011,
13, 1092-1094.

Thio FCMA intermediates, generated from the reactions of thioacids with
isonitriles, are active acyl donors, that form amide bonds under neutral
conditions.
Y. Rao, X. Li, S. J. Danishefsky, J. Am. Chem. Soc., 2009,
131, 12924-12926.

Microwave reactions of primary and secondary amines with
imidoylbenzotriazoles gave various polysubstituted amidines in good yields.
Convenient preparations of a variety of amides and imidoylbenzotriazoles
have also been developed using microwave irradiation under mild conditions
and short reaction times.
A. R. Katritzky, C. Cai, S. K. Singh, J. Org. Chem., 2006,
71, 3375-3380.

Various alcohols, phenols, amines and thiols
may easily be converted into acetate derivatives by treatment
with acetic anhydride in the presence of
acetonyltriphenylphosphonium bromide in good yields at room
temperature. With the same precatalyst, both aliphatic and aromatic aldehydes
can be transformed into the corresponding gem-diacetates under reflux
conditions.
A. T. Khan, L. H. Choudry, S. Ghosh, Eur. J. Org. Chem., 2005,
2782-2787.

Acyl halide-methanol mixtures are efficient reagents for the one-pot
transformation of t-butyl carbamates into amides. This transformation
can be carried out in the presence of a benzyloxycarbonyl group.
A. Nazih, D. Heissler, Synthesis,
2002, 203-206.

An efficient dynamic kinetic resolution of amines combines a ruthenium-catalyzed racemization with a lipase-catalyzed
resolution. A variety of primary amines were transformed into
one enantiomer of the amide in high yield and high enantioselectivity.
J. Paetzold, J. E. Bäckvall, J. Am. Chem. Soc.,
2005,
127, 17620-17621.

A practical procedure for an efficient dynamic kinetic resolution of primary
amines employs a palladium nanocatalyst as racemization catalyst, a commercial
lipase as resolution catalyst, and ethyl acetate or ethyl methoxyacetate as acyl
donor. Various amines and one amino acid amide have been resolved with good
yields and high enantiomeric excesses.
M.-J. Kim, W.-H. Kim, K. Han, Y. K. Choi, J. Park, Org. Lett., 2007,
9, 1157-1159.

A practical procedure for an efficient dynamic kinetic resolution of primary
amines employs a palladium nanocatalyst as racemization catalyst, a commercial
lipase as resolution catalyst, and ethyl acetate or ethyl methoxyacetate as acyl
donor. Various amines and one amino acid amide have been resolved with good
yields and high enantiomeric excesses.
M.-J. Kim, W.-H. Kim, K. Han, Y. K. Choi, J. Park, Org. Lett., 2007,
9, 1157-1159.

A mild, versatile, copper-catalyzed three-component coupling of organoindium reagents
with imines and acid chlorides provides α-substituted amides or N-protected amines in a single step with the sole byproduct
being indium trichloride.
D. A. Black, B. A. Arndtsen, Org. Lett.,
2006,
8, 1991-1993.

A simple, practical, and catalytic method for the N-formylation in the presence
of molecular iodine as a catalyst under solvent-free conditions is applicable to
a wide variety of amines. α-Amino acid esters can be converted without
epimerization.
J.-G. Kim, D. O. Jang, Synlett, 2010,
2093-2096.

A simple, mild method for N-formylation in the presence of indium metal
as a catalyst under solvent-free conditions is applicable to the chemoselective
reaction of amines and α-amino acid esters without epimerization.
J.-G. Kima, D. O. Jang, Synlett, 2010,
1231-1234.

A mild, simple, and selective N-formylation of amines with formic
acid in the presence of ZnO under solvent-free conditions gives products in
excellent yields.
M. Hosseini-Sarvari, H. Sharghi, J. Org. Chem., 2006,
71, 6652-6654.

Various tertiary benzanilide derivatives were effectively synthesized in high
yields from a broad range substituted benzoic acid and N-monoalkylated
anilines using dichlorotriphenylphosphorane in chloroform. Allyl, Boc, MPM and
the Z group were unaffected under these conditions.
I. Azumaya, T. Okamoto, F. Imabeppu, H. Takayanagi,
Tetrahedron, 2003, 59, 2325-2331.

In the presence of sodium acetate, the reaction between 2,2,6-trimethyl-4H-1,3-dioxin-4-one
and secondary or tertiary alcohols or primary or secondary amines could be
carried out in refluxing tetrahydrofuran. Under these much milder conditions,
side products were avoided, and β-keto esters and β-ketoamides were normally
obtained in quantitative yields.
V. Sridharan, M. Ruiz, J. C. Menéndez, Synthesis, 2010,
1053-1057.

An amidation of unactivated esters with amino alcohols catalazyed by a
stable nitrogen-heterocyclic carbene is described. The mechanism is
discussed.
M. Movassaghi, M. A. Schmidt, Org. Lett., 2005,
7, 2373-2376.

LiNTf2 is able to activate cyclic esters towards ring opening with a
stoichiometric amount of amines, thus leading to clean open-chain amides under
mild conditions. The generality of the method was demonstrated by a range of
selected lactones and amines.
C. Lalli, A. Trabocchi, G. Menchi, A. Guarna, Synlett, 2008,
189-192.

A small library of α,β-unsaturated oxindoles was
prepared by an efficient microwave-assisted one-pot sequence comprising an
aromatic substitution followed by an ionic Horner-Wadsworth-Emmons olefination.
A. Teichert, K. Jantos, K. Harms, A. Studer, Org. Lett., 2004,
6, 3477-3480.

Various alcohols, amines and N-hydroxylamines gave corresponding
formylated adducts in high yields by treatment with 2,2,2-trifluoroethyl
formate (TFEF). Chemoselective formylation of a primary amine could be readily
achieved in the presence of an unprotected primary alcohol.
D. R. Hill, C.-N. Hsiao, R. Kurukulasuriya, S.
Wittenberger, Org. Lett., 2002, 4, 111-113.

Deoxo-Fluor is a versatile and
mild reagent for acyl fluoride generation and subsequent one-flask amide
coupling. The conversion of acids to amides and Weinreb amides and the use
of Deoxo-Fluor as peptide-coupling reagent have been explored. Products were
isolated after facile purification in good yields.
J. M. White, A. R. Tunoori, B. J. Turunen, G. I.
Georg, J. Org. Chem., 2004, 69, 2573-2576.

A stereoconservative protection and deprotection method
of amino and carboxyl groups includes the generation of N-Phthaloyl N'-alkyl
secondary amides from N-phthaloyl amino acids by using a mixed anhydride method. These secondary
amides have been transformed by thermal rearrangement of the intermediate nitrosoamides
to esters with retention of configuration and excellent yields.
D. M. Shendage, R. Froehlich, G. Haufe, Org. Lett., 2004, 6,
3675-3678.

A mild and efficient oxidative amidation of aldehydes uses amine HCl salts
and tert-butyl hydroperoxide as an oxidant in the presence of a
copper catalyst.
W.-J. Yoo, C.-J. Li, J. Am. Chem. Soc., 2006,
128, 13064-13065.

Formation of N-alkenyl alkynylamides by N-acylation of imines with
alkynoyl chlorides and the subsequent cationic Au(I)/PPh3-catalyzed
cycloisomerization allows a convergent and rapid assembly of substituted
2-pyridones.
H. Imase, K. Noguchi, M. Hirano, K. Tanaka, Org. Lett.,
2008,
10, 3563-3566.




