Alkenes Wohl-Ziegler reaction

A second general method involves the bromination of alkenes with jY-bromosuccinimide (the Wohl-Ziegler reaction). A radical-chain reaction takes place between A-bromosuccinimide (NBS) and alkenes, which com-... 

The direct introduction of bromine into the allylic position of an alkene using ZV-bromosuccinimide is known as the Wohl-Ziegler reaction. Bromination is carried out in anhydrous reagents (to avoid hydrolysis of the bromoimide), usually boiling carbon tetrachloride or chloroform solution. The progress of the reaction can be followed by the fact that at first the dense N-bromosuccinimide is at the bottom of the flask and is gradually replaced by succinimide, which rises... 

In the first propagation step of the Wohl-Ziegler bromination, the bromine atom abstracts a hydrogen atom from the allylic position of the alkene and thereby initiates a substitution. This is not the only reaction mode conceivable under these conditions. As an alternative, the bromine atom could react with the C=C double bond and thereby start a radical addition to it (Figure 1.27). Such an addition is indeed observed when cyclohexene is reacted with a Br2/AIBN mixture. 

When unsymmetric alkenes are reacted under the Wohl-Ziegler conditions, product mixtures can be obtained. For example, reaction of 1-octene (27) gave about a 3 1 mixture of primary and secondary bromination products 28 and 29. ... 

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