Categories: C-O Bond Formation >
Synthesis of carbamates by carbamoylation
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.
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, 83, 913-920.
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.
A tin-catalyzed transcarbamoylation of primary and secondary alcohols with phenyl carbamate proceeds smoothly in toluene at 90˚C to generate the corresponding carbamates in good yields. This mild method exhibits a broad functional-group tolerance.
Y. Ichikawa, Y. Morishita, S. Kusaba, N. Sakiyama, Y. Matsuda, K. Nakano, H. Kotsuki, Synlett, 2010, 1815-1818.
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.
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.
J. A. Grzyb, M. Shen, C. Yoshina-Ishii, W. Chi, R. S. Brown, R. A. Batey, Tetrahedron, 2005, 61, 7153-7175.
A catalytic amount of N-methylimidazole (NMI) accelerated a mild one-pot synthesis of aromatic and aliphatic carbamates via the Lossen rearrangement. Moreover, the utility of arylsulfonyl chloride in combination with NMI minimizes the formation of often-observed hydroxamate-isocyanate dimers.
S. Yoganathan, S. J. Miller, Org. Lett., 2013, 15, 602-605.
An efficient synthesis of aryl carbamates - including major carbamate protecting groups - was achieved by introducing alcohols into the reaction of palladium-catalyzed cross-coupling of aryl chlorides and triflates with sodium cyanate. This methodology also provides direct access to S-thiocarbamates and diisocyanate precursors to polyurethane materials.
E. V. Vinogradova, N. H. Park, B. P. Fors, S. L. Buchwald, Org. Lett., 2013, 15, 1394-1397.
A convenient one-pot method allows the conversion of phenylisocyanate into ortho-functionalized aniline derivatives. The reaction proceeds via a selective ortho-metalation of a transient labile urea, which can be considered as a synthetic equivalent of 2-lithio-phenylisocyanate, a highly improbable intermediate.
C. E. Houlden, G. C. Lloyd-Jones, K. I. Brooker-Milburn, Org. Lett., 2010, 12, 3090-3092.
The reaction of Grignard reagents with alkyl imidazolecarboxylates, which were prepared from alcohols with carbonyl diimidazole, gave the corresponding esters in good to excellent yields.
T. Werner, A. G. M. Barrett, J. Org. Chem., 2006, 71, 4302-4304.
Acyl isocyanates generated by the reaction of primary amides with oxalyl chloride react with a wide range of amides, hydrazides, amines, alcohols, carbazate, and sulfonate to provide symmetrical and unsymmetrical diacyl urea derivatives, acyl ureas/carbamates/thiocarbamates, and related compounds. This convenient one-pot, two-step synthesis uses cheap and commercially available starting reagents.
A. G. Hernandez, G. M. Grooms, A. T. El-Alfy, J. Stec, Synthesis, 2017, 49, 2163-2176.