Curtius rearrangement template

Benzoyl azide (resonance form with N⁻–N⁺≡N) loses N₂ as phenyl migrates to nitrogen; methanol adds to the isocyanate to give methyl N-phenylcarbamate.

Mechanism step by step

An acyl azide loses N₂ and rearranges to an isocyanate, trapped as a carbamate

1. Resonance form – The acyl azide as N⁻–N⁺≡N
2. Rearrangement – Phenyl moves to N as N₂ leaves (concerted)
3. Methanol adds – Attack on the isocyanate carbon
4. Proton transfer – The carbamate

Key points

• The acyl azide comes from an acyl chloride and NaN₃ (or DPPA with the acid).
• Migration keeps the configuration of the migrating carbon.
• Water instead of an alcohol gives the amine (via the carbamic acid and loss of CO₂).
• Related: Hofmann (N-bromoamide) and Lossen (hydroxamic acid) rearrangements.

Drawn with 113 atoms, 14 arrows, 6 shapes – every one editable in MolDraw.

Sources

• Curtius, Ber. Dtsch. Chem. Ges. 1890, 23, 3023 Original paper
• Kürti & Czakó, Strategic Applications of Named Reactions in Organic Synthesis, Elsevier 2005 Textbook
• Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012 Textbook