4-Quinolone bromination

This coupling works best when the halogen at the 7-position is bromine rather than chlorine or fluorine. This represents the first appUcation of this coupling reaction to the intact quinoline nucleus and thus represents an important advance in quinolone chemistry. 

Among the nucleophilic processes available for introduction of bromine to quinolines are reactions of the diazonium salts (87JHC181) and syntheses based on hydroxyquinolines or quinolones (91M935) (Scheme 36). The former processes are especially useful for making 5-, 6-, 7-, and 8-bromo derivatives. Halogen-halogen exchange reactions have also been reported, but they are not common. When perfluoroquinoline was heated... 

There are many examples of brominations of 2-quinolones and other... 

Table 4 Results of the bromination of 2-quinolones under various conditions, including...

Scheme 12 Bromination of 2-quinolones using NBS and microwave irradiation...

When position 6 on the 2-quinolone is blocked, bromination takes place selectively at the 3-position. Thus, microwave irradiation of 45 in acetonitrile at 150 °C for 50 min afforded the 3-bromo-quinolin-2(lff)-one 46 in 87% yield (Scheme 12). 

Bromine in chloroform added dropwise to a soln. of 4-niethyl-3-vinyl-2-quinolone in the same solvent, then treated with triethylamine and refluxed 1 hr. -> 4-methylfuro[2,3-b]quinoline. Y 88%. P. Shanmugam, P. Lakshminarayana, and R. Palaniappan, M. 104, 633 (1973). 

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