Wohl-Ziegler Bromination

• General Characteristics

-The Wohl-Ziegler reaction is the free radical-based bromination of allylic and benzylic positions using N-bromosuccinimide (NBS). The solvents stable under free radical conditions such as carbon tetrachloride are used.

-The bromination occurs at the internal positions rather than the terminal positions following the relative stability of free-radical intermediates.

• General References

・Wohl, A. Ber. 1919, 52, 51. doi:10.1002/cber.19190520109
・Ziegler, K. et al. Ann. 1942, 551, 1. doi:10.1002/jlac.19425510102
・Djerassi, C. Chem. Rev. 1948, 43, 271. DOI: 10.1021/cr60135a004
・Horner, L.; Winkelman, E. M. Angew. Chem. 1959, 71, 349. doi:10.1002/ange.19590711102

• Reaction Mechanism

The actual bromination agent is the molecular Br₂ present in the system and not NBS. Side reactions are inevitable when there is excess bromine in the system.

• Examples

An example where the internal position is brominated preferentially over the terminal position.^[1]

• Experimental Procedure

• Experimental Tips

• References

[1] Greenwood, F.L.; Kellert, M. D.; Sedlak, J. Org. Synth. 1958, 38, 8. [website]

• Related Books

 

 

 

bromination, free radical, n-bromosuccinimide