Enolizable ketones bromination

When bromination of the enolizable ketone is conducted in glycol, simultaneous monobromination and acetalization is observed [2]. 1,5-Dicarbonyl compounds react with benzyltrimethylammonium dichloroiodate to yield initially a monochloro derivative, which undergoes ring closure to produce a 2-substituted 5-acylfuran [26],... 

Selected examples of the bromination of enolizable ketones R COCLLR2... 

Example (ii) starts with a Grignard addition to a nitrile and hydrolysis of the imine to a ketone 501). Bromination in acid solution at the only enolizable position gives the product. 

Ketones containing an enolizable hydrogen can be halogenated at the a position (the carbon adjacent to the carbonyl) with bromine, chlorine, NBS, or NCS. The reaction probably proceeds via addition of X2 to the enol form of the carbonyl (secs. 9.2.A, 9.8.A). Elimination of HX from the addition product generates an other enol, which tautomerizes to the a-haloketone. Reaction of cyclohexanone with bromine, for example, would give 2-bromocyclohexanone (174) and a similar reaction with NCS (173) would give 2-chloro-cyclohexanone (172). 

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