Ketones, halogenation orientation

Enolization is the rate-determining step in the halogenation of normal ketones. Where alternate directions for enolization exist, the preferred direction (and hence the position of kinetic bromination) depends on the substituents and stereochemistry. Furthermore, the orientation of the bromine introduced depends on stereochemical and stereoelectronic factors. 

Electrophilic addition of hydrogen halides to a,/f-unsaturated aldehydes and ketones places the halogen on the /3 carbon. This orientation is opposite to that observed for related additions to conjugated dienes ... 

The reactions of allyliron tricarbonyl halides with donor molecules were studied. Triphenylphosphine substituted only one carbonyl, that trans-oriented with respect to the halogen of the form (XIX) [432). The phosphine derivatives of (XX) were not isolated as pure compounds. The complexes were decomposed entirely by dimethyl sulfoxide, giving [(0113)280] jFeX2 [435). Thermal decomposition of C3H5Fe(CO)3X depended on the medium and gave either diallyl, or diallyl ketone, together with propene, allyl ether, Fe(CO)5, and FeX2 [436). 

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