The Wolff rearrangement uses either catalytic silver oxide, heat, or light to convert an α-diazo ketone to a ketene. In a one-step reaction, the catalyst initiates a 1,2-shift to release nitrogen gas and produce ketene. Due to the release of nitrogen gas, this reaction should not be performed in a closed system.

• Thermal catalysis is not ideal as delicate substrates may degrade and side reactions such as the direct displacement of the diazo group without rearrangement frequently occur. ^[1]
• Photochemical activation is convenient and takes place even at low temperatures, but only if the product is not photolabile. ^[1]
• Silver catalysts are generally used as they lower the required reaction temperature considerably compared to the thermal process. ^[1]
• If the migrating group has a stereocenter, there is net retention of configuration after the migration. ^[1]
• Cyclic diazo ketones undergo ring-contraction. ^[1]
• Numerous side reactions are possible since α-diazo ketones are very reactive. Careful choice of reaction conditions can avoid/minimize these side reactions. ^[2,3]

• Reagents: Catalytic Ag₂O/silver(I) benzoate or Δ or light
• Reactant: α-Diazo Ketone
• Product: Ketene
• Type of Reaction: Rearrangement
• Bond Formation: O=C=C

Mechanism

Original Paper

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