Categories: C-N Bond Formation >
Synthesis of urea derivatives
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Recent Literature
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
gave acyl azides by reaction with iodine azide at 0 - 25°C. If the reaction
is performed at reflux Curtius rearrangement occurs and carbamoyl azides are
obtained directly from the aldehyde in 70-97% yield.
L. Marinescu, J. Thinggaard, I. B. Thomsen, M. Bols,
J. Org. Chem., 2003, 68, 9453-9455.
Carbamates may 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.
