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.

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.

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.

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.