Categories: C-N Bond Formation >
Synthesis of urea derivatives
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General procedures allow the carbonylation of aliphatic amines by employing
S,S-dimethyl dithiocarbonate (DMDTC) as a phosgene substitute to yield N-alkylureas,
N,N′-dialkylureas (both symmetrical and unsymmetrical), and N,N,N′-trialkylureas.
All reactions were carried out in water.
E. Artuso, I. Degani, R. Fochi, C. Magistris, Synthesis, 2007,
3497-3506.

A one pot reaction of carbonylimidazolide in water with a nucleophile provides
an efficient and general method for the preparation of urea, carbamates and
thiocarbamates without an inert atmosphere. Products precipitate out from the
reaction mixture and can be obtained in high purity by filtration.
K. J. Padiya, S. Gavade, B. Kardile, M. Tiwari, S. Bajare, M. Mane, V. Gaware,
S. Varghese, D. Harel, S. Kurhade, Org. Lett., 2012,
14, 2814-2817.

With ambient pressure of carbon monoxide and oxygen at room temperature, N,N-dialkyl-N′-arylureas
were selectively accessible from secondary amines, aromatic amines, and sulfur
in very good yields.
T. Mizuno, T. Nakai, M. Mihara, Synthesis, 2009,
2492-2496.

An efficient method for palladium-catalyzed cross-coupling of aryl chlorides
and triflates with sodium cyanate allows the
synthesis of unsymmetrical N,N′-di- and N,N,N′-trisubstituted ureas in one pot
and is tolerant of a wide range of functional groups. Insight into the mechanism
of aryl isocyanate formation was gleaned through studies of the transmetalation
and reductive elimination steps of the reaction.
E. V. Vinogradova, B. P. Fors, S. L. Buchwald, J. Am. Chem. Soc., 2012,
134, 11132-11135.

1-Propanephosphonic acid cyclic anhydride (T3P) promotes the synthesis of
hydroxamic acids from carboxylic acids. Application of ultrasonication
accelerates this conversion. Further, T3P has also been employed to activate the
hydroxamates, leading to isocyanates via Lossen rearrangement. Trapping with
suitable nucleophiles affords the corresponding ureas and carbamates.
B. Vasantha, H. P. Hemantha, V. V. Sureshbabu, Synthesis, 2010,
2990-2996.

Carbonyldiimidazole mediates the Lossen rearrangement of various hydroxamic
acids to isocyanates. This process is experimentally simple and mild, with
imidazole and CO2 being the sole stoichiometric byproduct. The method
avoids the use of hazardous reagents and thus represents a green alternative to
standard processing conditions for the Curtius and Hofmann rearrangements.
P. Dubé, N. F. F. Nathel, M. Vetelino, M. Couturier, C. L. Abossafy, S.
Pichette, M. L. Jorgensen, M. Hardink, Org. Lett., 2009,
11, 5622-5625.

A smooth and efficient oxidation of isonitriles to isocyanates by DMSO as the
oxidant is catalyzed by trifluoroacetic anhydride. The process is complete in a
few minutes, forming dimethyl sulfide as the only byproduct. The newly formed
isocyanates may be used directly or isolated in high purity by solvent
evaporation.
H. V. Le, B. Ganem, Org. Lett., 2011,
13, 2584-2585.

Zirconium(IV)-catalyzed exchange processes of dialkyl carbonates and carbamates
in the presence of amines gave carbamates and ureas using 2-hydroxypyridine (HYP)
and 4-methyl-2-hydroxyquinoline (MeHYQ) as catalytic additives, respectively. A
microwave acceleration effect was observed in Zr(IV)-catalyzed carbamate-urea
exchange.
C. Han, J. A. Porco, Jr, Org. Lett., 2007,
9, 1517-1520.

Selective and convenient syntheses of carbamates, symmetric ureas, and
unsymmetrical ureas have been accomplished by the reaction of amines with phenyl
4,5-dichloro-6-oxopyridazine-1(6H)-carboxylate as a carbonyl source under
mild conditions.
H.-G. Lee, M.-J. Kim, S.-E. Park, J.-J. Kim, S.-G. Lee, Y.-J. Yoon, Synlett, 2009,
2809-2814.

A facile one-pot procedure for the synthesis of urea-linked peptidomimetics and
neoglycopeptides under Curtius rearrangement conditions employing Deoxo-Fluor
and TMSN3 is efficient and circumvents the isolation of acyl azide
and isocyanate intermediates. The reaction was carried out under ultrasonication.
H. P. Hemantha, G. Chennakrishnareddy, T. M. Vishwanatha, V. V. Sureshbabu, Synlett, 2009,
407-410.

The reaction of di-tert-butyl dicarbonate or a chloroformate and
sodium azide with an aromatic carboxylic acid produces the corresponding
acyl azide. The acyl azide undergoes a Curtius rearrangement to form an
isocyanate derivative which is trapped either by an alkoxide or by an amine
to form the aromatic carbamate or urea.
H. Lebel, O. Leogane, Org. Lett., 2006,
8, 5717-5720.

Readily prepared carbamoylimidazolium salts act as efficient N,N-disubstituted
carbamoylating reagents, as a result of the ‘imidazolium’ effect. The salts
react with amines, thiols, phenols/alcohols, and carboxylic acids in high yields,
without the need for subsequent chromatographic purification of the products,
producing ureas, thiocarbamates, carbamates, and amides, respectively.
M. B. Bertrand, J. P. Wolfe, Tetrahedron, 2005,
61, 6447-6459.

M. B. Bertrand, J. P. Wolfe, Tetrahedron, 2005,
61, 6447-6459.

High-yielding reductive alkylation of electron-deficient o-haloarylamines
followed by treatment with inexpensive N-chlorosulfonyl isocyanate
afforded primary ureas in good overall yields. A Pd-catalyzed urea
cyclization reaction furnished imidazopyridinones and benzoimidazolones in
excellent yields.
M. McLaughlin, M. Palucki, I. W. Davies, Org. Lett.,
2006,
8, 3311-3314.

Imidazolidin-2-ones are prepared in two steps from readily available N-allylamines.
Addition of the amine starting materials to isocyanates affords N-allylureas,
which are converted to imidazolidin-2-ones with generation of two bonds and
up to two stereocenters in the presence of aryl bromides, a catalytic amount
of Pd2(dba)3/Xantphos and NaOtBu.
J. A. Fritz, J. S. Nakhla, J. P. Wolfe, Org. Lett.,
2006,
8, 2531-2534.

Aliphatic and aromatic aldehydes can be converted to acyl azides by treatment
with iodine azide. If the reaction is performed at reflux, Curtius rearrangement
occurs and carbamoyl azides are obtained directly from the aldehyde in good yield.
L. Marinescu, J. Thinggaard, I. B. Thomsen, M. Bols,
J. Org. Chem., 2003, 68, 9453-9455.

The reaction of carbamoyl azides with hydroxylamine leads to N-hydroxyureas,
whereas the reaction of carbamoyl cyanides with hydroxylamine gives carbamoyl
amidoxime derivatives. The latter type of compound represents an interesting
precursor for heterocyclic structures.
J. Paz, C. Pérez-Balado, B. Iglesias, L. Muñoz, J. Org. Chem., 2010,
75, 8039-8047.

Carbamates can be converted into ureas using aluminum amide complexes. Bi-, tri-
and tetra-substituted ureas were prepared from carbamate-protected primary or
secondary amines by reaction with primary or secondary amines in the presence of
stoichiometric quantities of trimethylaluminum.
S.-H. Lee, H. Matsushita, B. Clapham, K. D. Janda, Tetrahedron, 2004,
60, 3439-3443.

