Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/Named Reactions/Curtius Rearrangement

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The Curtius rearrangement (or Curtius reaction or Curtius degradation), as first defined by Theodor Curtius, is a chemical reaction that involves the rearrangement of an acyl azide to an isocyanate.[1][2] Several reviews have been published.[3][4]

The Curtius rearrangement

The isocyanate can be trapped by a variety of nucleophiles. Often water is added to hydrolyze the isocyanate to an amine.[5] When done in the presence of tert-butanol, the reaction generates Boc-protected amines, useful intermediates in organic synthesis.[6][7]

Carboxylic acids 1 can be easily converted to acyl azides 3 using diphenylphosphoryl azide 2.[8][9][10]

Using DPPA to convert an acid to a BOC-protected amine

Likewise, when the Curtius reaction is performed in the presence of benzyl alcohol, Cbz-protected amines are formed.[11]

Reaction mechanism[edit | edit source]

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).

The mechanism of the Curtius rearrangement

Scope[edit | edit source]

In one variation called the Darapsky degradation (A. Darapsky, 1936) a Curtius rearrangement takes place as one of the steps from an α-cyanoester to an amino acid.[12]

References[edit | edit source]

  1. ↑ Curtius, T. (1890). Ber. 23: 3023. {{cite journal}}: Missing or empty |title= (help)
  2. ↑ doi:10.1002/prac.18940500125
  3. ↑ Smith, P. A. S. (1946). Org. React. 3: 337–449. {{cite journal}}: Missing or empty |title= (help)
  4. ↑ doi:10.1021/cr00084a001
  5. ↑ Kaiser, C.; Weinstock, J. (1988), "Amines from mixed carboxylic-carbonic anhydrides: 1-phenylcyclopentylamine", Org. Synth.{{citation}}: CS1 maint: multiple names: authors list (link); Coll. Vol., 6: 910 {{citation}}: Missing or empty |title= (help)
  6. ↑ doi:10.1021/op970115w
  7. ↑ doi:10.1021/ol051428b
  8. ↑ Shioiri, T.; Yamada, S. (1990), "Diphenyl phosphorazidate", Org. Synth.{{citation}}: CS1 maint: multiple names: authors list (link); Coll. Vol., 7: 206 {{citation}}: Missing or empty |title= (help)
  9. ↑ doi:10.1021/ja00772a052
  10. ↑ doi:10.1016/S0040-4020(01)97352-1
  11. ↑ Jessup, P. J.; Petty, C. B.; Roos, J.; Overman, L. E. (1988), "1-N-Acylamino-1,3-dienes from 2,4-pentadienoic acids by the Curtius rearrangement: benzyl trans-1,3-butadiene-1-carbamate", Org. Synth.{{citation}}: CS1 maint: multiple names: authors list (link); Coll. Vol., 6: 95 {{citation}}: Missing or empty |title= (help)
  12. ↑ http://www.chempensoftware.com/reactions/RXN051.htm
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