Categories: C-N Bond Formation >
Synthesis of carbamates
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.
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.
N-Substituted carbamoyl chlorides can be formed in situ and subsequently reacted with substituted phenols to avoid the direct manipulation of sensitive reactants. This simple, versatile, one-pot procedure for the synthesis of substituted O-aryl carbamates offers an economical and efficient route to many compounds of interest.
S. E. Varjosaari, P. Suating, M. J. Adler, Synthesis, 2016, 48, 43-47.
An efficient, one-pot procedure for the Hofmann rearrangement of aromatic and aliphatic amides provides methyl and benzyl carbamates in high yields in the presence of N-bromoacetamide and lithium hydroxide or lithium methoxide. β-Phenylamino amides gave five-membered cyclic ureas stereospecifically.
I. I. Jevtić, L. Došen-Mićović, E. R. Ivanović, M. D. Ivanović, Synthesis, 2016, 48, 1550-1560.
In a mild and metal-free synthesis of aryl isocyanates from arylamines, a carbamic acid intermediate, derived from the arylamine starting material and CO2 in the presence of DBU, is dehydrated by activated sulfonium reagents to generate the corresponding isocyanate. The latter can be trapped by various amines and alcohols to make unsymmetrical ureas and carbamates, respectively.
Y. Ren, S. A. L. Rousseaux, J. Org. Chem., 2018, 84, 913-920.
Stable Fmoc-, Boc-, and Alloc-benzotriazoles react with various amino acids including unprotected serine and glutamic acid, in the presence of triethylamine at 20˚C to afford Fmoc-, Boc-, and Alloc-protected amino acids in very good yields free of dipeptide and tripeptide impurities. Fmoc-, and Alloc-Gly-Gly-OH dipeptides were prepared in excellent yields by N-acylation of glycylglycine.
T. S. Ibrahima, S. R. Tala, S. A. El-Feky, Z. K. Abdel-Samii, A. R. Katritzky, Synlett, 2011, 2013-2016.
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 nickel boride catalyzed reduction of nitriles allows the preparation of Boc protected amines. The catalytic use of nickel(II) chloride in combination with excess sodium borohydride is environmental benign and tolerates air and moisture. Although the yield is sometimes moderate, the cleanliness of the method is exceptional.
S. Caddick, D. B. Judd, A. K. de K. Lewis, M. T. Reich, M. R. V. Williams, Tetrahedron, 2003, 59, 5417-5423.
A selective cathodic reduction of carbon dioxide in CO2-saturated room-temperature ionic liquid BMIm-BF4 solutions containing amines, followed by addition of EtI as an alkylating agent allows an environmentally friendly, mild, and safe synthesis of organic carbamates in good yields.
M. Feroci, M. Orsini, L. Rossi, G. Sotgiu, A. Inesi, J. Org. Chem., 2007, 72, 144-149.
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.
Tert-butyl carbamates are produced in high yields at low temperature by the reaction of a carboxylic acid with di-tert-butyl dicarbonate and sodium azide, which leads to an acyl azide intermediate. Subsequent Curtius rearrangement in the presence of tetrabutylammonium bromide and zinc(II) triflate and trapping of the isocyanate derivative gives the desired product. This method tolerates various functional groups.
H. Lebel, O. Leogane, Org. Lett., 2005, 7, 4107-4110.
Demethylation of N,N-dimethylanilines was carried out in various ionic liquids and acetonitrile as well as under solvent-free conditions. The reactivity dramatically depends on the employed solvent, with [bmim]Cl showing the best reactivity.
S. Imoria, H. Togo, Synlett, 2006, 2629-2632.
An efficient one-pot procedure for the zinc-mediated reduction of nitroarenes in the presence of chloroformates leads to the corresponding N,O-bisprotected hydroxylamines in good yield under ambient conditions in THF-water mixtures. Solvolysis of the bisprotected hydroxylamines with sodium methoxide at room temperature provides access to synthetically versatile N-aryl-N-hydroxy carbamates in excellent yields.
A. Porzelle, M. D. Woodrow, N. C. O. Tomkinson, Synlett, 2009, 798-802.