Wolff Rearrangement
Wolff Rearrangement
The Wolff rearrangement is a chemical reaction in organic chemistry that involves the conversion of an α-diazocarbonyl compound into a ketene, with the concomitant loss of dinitrogen and a 1,2-rearrangement of the molecular structure. This reaction is named after Ludwig Wolff, who discovered it in 1902[1].
Mechanism and Conditions
The mechanism of the Wolff rearrangement has been a topic of debate, with evidence supporting both concerted and stepwise pathways. In the concerted mechanism, the loss of dinitrogen and the 1,2-shift occur simultaneously, while in the stepwise mechanism, an electron-deficient carbene intermediate is formed first, followed by the 1,2-shift[1][3][5][6][7][8][9][11][12][13].
The rearrangement can be induced under various conditions:
- Thermolysis: Heating the α-diazocarbonyl compound can initiate the rearrangement[1][3][7].
- Photolysis: Exposure to light, particularly UV light, can also induce the reaction[1][3][6][7].
- Transition Metal Catalysis: The use of transition metal catalysts, especially silver (I) oxide or other Ag(I) catalysts, can facilitate the reaction[1][7][8].
Applications and Synthetic Utility
The Wolff rearrangement is particularly useful in synthetic organic chemistry due to the versatility of the ketene intermediate. Ketenes can undergo nucleophilic attack by weakly acidic nucleophiles such as water, alcohols, and amines to form carboxylic acid derivatives. They can also participate in [2+2] cycloaddition reactions to form four-membered rings[1][3][4][6][7][8].
A specific application of the Wolff rearrangement is the Arndt-Eistert homologation, which allows for the elongation of a carboxylic acid by a methylene unit. This process involves the sequential addition of thionyl chloride, diazomethane, and silver(I) nitrate[3][5][6][13].
Stereochemistry and Migratory Aptitude
The stereochemistry of α-diazocarbonyl compounds plays a crucial role in the mechanism of the Wolff rearrangement. These compounds typically exist in an equilibrium between s-cis and s-trans conformers, which can influence the reaction pathway. Generally, s-cis conformers react in a concerted manner, while s-trans conformers may proceed through a carbene intermediate or not rearrange at all[1][5].
The migratory aptitude of different groups during the rearrangement has been studied, with the general trend for thermal rearrangements being H > aryl ≥ alkyl, and for photochemical rearrangements being H > alkyl ≥ aryl > SR > OR ≥ NR[5].
Limitations and Considerations
Despite its synthetic utility, the Wolff rearrangement has limitations due to the highly reactive nature of α-diazocarbonyl compounds, which can undergo a variety of competing reactions. Careful choice of reaction conditions is necessary to avoid or minimize these side reactions[7].
Historical Context
The reaction was not commonly used until 20 years after its discovery, as methods for facile diazo ketone synthesis were unknown until the 1930s. Since then, the Wolff rearrangement has been extensively reviewed and applied in various total syntheses[1].
Conclusion
The Wolff rearrangement remains a valuable tool in the synthesis of carboxylic acid derivatives and other compounds. Its versatility and the ability to retain stereochemistry during the migration make it a significant reaction in the field of organic synthesis.
Citations:
[1] https://en.wikipedia.org/wiki/Wolff_rearrangement
[2] https://www.youtube.com/watch?v=KOITQR54DfM
[3] https://employees.csbsju.edu/cschaller/Reactivity/rearr/ERwolff.htm
[4] https://www.sciencedirect.com/topics/chemistry/wolff-rearrangement
[5] https://thesis.library.caltech.edu/5378/49/%282A1%29_WCb.pdf
[6] https://chem.libretexts.org/Bookshelves/General_Chemistry/Book:_Structure_and_Reactivity_in_Organic_Biological_and_Inorganic_Chemistry_%28Schaller%29/V:__Reactivity_in_Organic_Biological_and_Inorganic_Chemistry_3/11:_Electrophilic_Rearrangement/11.05:_Wolff_Rearrangement
[7] https://www.jk-sci.com/blogs/resource-center/wolff-rearrangement
[8] https://www.organic-chemistry.org/namedreactions/wolff-rearrangement.shtm
[9] https://www.name-reaction.com/wolff-rearrangement
[10] https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/wolff-rearrangement
[11] https://www.rsc.org/publishing/journals/prospect/ontology.asp?id=RXNO%3A0000051
[12] https://chemistryscore.com/wolff-rearrangement/
[13] https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Book:_Virtual_Textbook_of_OChem_%28Reusch%29_UNDER_CONSTRUCTION/30:_Cationic_Rearrangements/30.9:_Rearrangements_of_Acyl_Carbenes