The Curtius rearrangement, as first defined by Theodor Curtius, is a chemical reaction that involves the rearrangement of an acyl azide to an isocyanate. Several reviews have been published.

The isocyanate can be trapped by a variety of nucleophiles. Often water is added to hydrolyze the isocyanate to an amine. When done in the presence of tert-butanol, the reaction generates Boc-protected amines, useful intermediates in organic synthesis.

Carboxylic acids 1 can be easily converted to acyl azides 3 using diphenylphosphoryl azide 2.

Likewise, when the Curtius reaction is performed in the presence of benzyl alcohol, Cbz-protected amines are formed.

Reaction mechanism

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The first step of the Curtius rearrangement is the loss of nitrogen gas forming an acyl nitrene (2). Once formed, acyl nitrenes very quickly rearrange by migration of R-group forming the desired isocyanate (3).

References

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1. Curtius, T. Ber. 1890, 23, 3023.
2. Curtius, T. J. Prakt. Chem. 1894, 50, 275.
3. Smith, P. A. S. Org. React. 1946, 3, 337-449. (Review)
4. Scriven, E. F.; Turnbull, K.; Chem. Rev. 1988, 88, 297-368. (Review)
5. Kaiser, C.; Weinstock, J. Organic Syntheses, Coll. Vol. 6, p.910 (1988); Vol. 51, p.48 (1971). (Article)
6. Ende, D. J. a.; DeVries, K. M.; Clifford, P. J.; Brenek, S. J. Org. Proc. Res. Dev. 1998, 2, 382-392.
7. Lebel, H.; Leogane, O.; Org. Lett. 2005, 7(19), 4107-4110. ()
8. Shioiri, T.; Yamada, S. Organic Syntheses, Coll. Vol. 7, p.206 (1990); Vol. 62, p.187 (1984). (Article)
9. Shioiri, T.; Ninomiya, K.; Yamada, S. J. Am. Chem. Soc. 1972, 94, 6203-6205.
10. Ninomiya, K.; Shioiri, T.; Yamada, S. Tetrahedron 1974, 30, 2151-2157.
11. Wolff, O.; Waldvogel, S. R. Synthesis 2004, 1303-1305.
12. Jessup, P. J.; Petty, C. B.; Roos, J.; Overman, L. E. Organic Syntheses, Coll. Vol. 6, p.95 (1988); Vol. 59, p.1 (1979). (Article)

See also

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• Lossen rearrangement
• Hofmann rearrangement
• Schmidt reaction
• Tiemann rearrangement

Organic reactions

Curtius-Reaktion | Curtius-omlegging | クルチウス転位