Synthesis of carbamates by carbamoylation

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

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

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.