Electrophilic reactions 1,1-dihaloalkenes

The Pd-catalyzed reaction of alkynylzincs with alkenyl electrophiles is generally dependable and widely applicable. However, recent studies with 1,1-dihalo-l-alkenes, 1,2-dihaloalkenes, and other alkenyl halides have indicated that the presence of two proximal... 

Electrophilic addition reactions are another dass of reactions that have been extensively studied in organic solvents from a mechanistic point of view and bromine addition is one of the most investigated addition reactions. Chiappe et al. have used ionic liquids to synthesize vidnal dihaloalkanes and dihaloalkenes by dectrophilic addition of halogens to double and triple bonds (Scheme 5.1-15) [48-50]. Recently, dibromides have also been synthesized [51] in ionic liquids using electrogenerated bromine, whereas bromohydrins have been obtained [52] under two-phase conditions (water/IL) through a vanadium (V) catalyzed oxidation of bromide ions by hydrogen peroxide. 

Similarly, 1,1-dihaloalkenes are versatile electrophiles that show a remarkable stereoselectivity in cross-coupling reactions. Pd-catalyzed coupHng with alkenylz-incs is trans selective and yields 2-halo-l,3-dienes with excellent stereochemical purity [182-185]. As illustrated with the preparation of 226, PdCljIDPEPhos) is a remarkable catalyst to perform this reaction [186] (Scheme 4.50). The 2-halo-1,3-diene products can then be engaged in a second Negishi cross-coupling reaction that shows a remarkable stereochemical behavior (Scheme 4.50). Typical... 

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