Coupling vinyl chlorides with Grignard reagents

As shown in Scheme 78, with or without zinc chloride, benzylic Grignard reagents couple with vinyl bromide to form allylbenzene derivatives in high ee (188). This method has been used to prepare optically active allylsilanes in up to 95% ee. Vinylic bromides with E configurations lead to the E allylsilanes with high ee, and Z bromides lead to Z allylsilanes with lower ee. 

Polarization also occurs in coupling and disproportionation reactions of Grignard reagents with alkyl halides. The vinyl protons of isobutene produced in the reaction of t-butylmagnesium chloride with t-butyl bromide show A/E polarization as do the methyl protons of isobutane (Ward et al., 1970). Similar results arise in the reaction of diethyl-magnesium with organic halides (Kasukhin et al., 1972). 

Asymmetric coupling of a vinyl halide with a Grignard reagent. 1-Phenylethyl-magnesium chloride couples with vinyl bromide in the presence of a nickelcatalyst (1) composed of NiCl, and (-)-norphos to give (S)-3-phenyl-l-butene (2) in 67% enantiomeric excess.1... 

A polystyrene-bound chiral aminophosphine-Ni(II) chloride complex catalyzes the asymmetric cross-coupling reaction of a secondary alkyl Grignard reagent with vinyl bromide in a moderate optical yield (25). 

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