Stereoselective halogenation reactions, in particular fluorinations, are not everyday's chemistry despite the fundamental and still increasing significance of fluorinated molecules, e.g., for the life science industry. The selective fluorination of a bioactive compound can be generally beneficial in terms of a possible increased intrinsic activity, enhanced chemical and metabolic stability, and improved pharmacokinetics. It is clear that more efficient and selective methodologies for the introduction of fluorine into organic molecules are still needed. We review in this article latest progresses in the area of enantioselective fluorinations, with particular emphasis on new catalytic reactions and extend our discussion to similar reactions involving the other halogens.

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Dichloroiodo)toluene ( dichloro(4-methylphenyl)iodine; 2) was found to be a suitable chlorinating agent in the catalytic asymmetric chlorination of b-keto esters 3 catalyzed by the [Ti(TADDOLato)] complex 1 ( bis(acetonitrile)dichloro[(4R,5R)-2,2-dimethyl-a,a,a',a'-tetra(naphthalen-1-yl)-1,3-dioxolane-4,5-dimethanolato(2 À)-kO,kO']titanium), whereby a-chlorinated products were obtained in moderate to good yields and enantioselectivities of up to 71% (Scheme 2, Table 2). The enantioselectivity of the reaction shows a remarkable temperature dependence, the maximum selectivity being obtained at ca. 508.

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The chlorination of readily available secondary and tertiary alkyl phenyl sulfides using (dichloroiodo)benzene (PhICl) is reported. This mild and rapid nucleophilic chlorination is extended to sulfa-Michael derived sulfides, affording elimination-sensitive β-chloro carbonyl and nitro compounds in good yields. The chlorination of enantioenriched benzylic sulfides to the corresponding inverted chlorides proceeds with high stereospecificity, thus providing a formal entry into enantioenriched chloro-Michael adducts. A mechanism implying the formation of a dichloro-λ-sulfurane intermediate is proposed.