Bromine reaction with vinylsilanes

For other vinylsilanes, the reaction with chlorine or bromine usually proceeds with inversion of configuration, i.e. the equilibrium A lies to the right. 

Bromine and chlorine react with vinylsilanes to afford vinyl bromide and chloride with net inversion of configuration. Addition of these halogens proceeds with anti stereochemistry. Elimination of halo-silane in the presence of a nucleophile like F or RO also is assumed to take place in an anti manner (Scheme 16). The same transformation using iodine is applicable only to 1,2-dialkylvinylsilanes. The process is a reliable method for the preparation of vinyl halides of defined configuration. The reactions are not, overall, reductions, and they are included here only to emphasize the usefulness of the products of hydrosilylation. 

Isomerically pure vinyl halides are important starting materials for preparation of the corresponding vinyl lithium species (see Section 7.1) and for use in Pd-catalyzed coupling reactions (see Section 7.10). Halogenation of vinylsilanes offers a valuable route for the synthesis of both (E)- and (Z)-vinyl halides. These reactions involve addition of the halogen to the double bond, followed by elimination of the silicon and halide moieties. The stereochemical outcome of the reaction will depend on both the mode of addition and the mode of elimination. For example, bromination of (Z)-vinylsilanes with bromine in CH2CI2 proceeds via an anti-addition. Treatment of the bromine adduct with sodium methoxide results in anti-desilicobromination. The conversion of the vinylsi-lane into the vinylbromide occurs with overall inversion of the double bond stereochemistry. " ... 

More practically, 2-pyridyl-substituted vinylsilanes themselves can be directly subjected to the reactions with various electrophiles. For example, treatment of 2-pyridyl-substituted vinylsilanes with acid chlorides in the presence of aluminum chloride affords the corresponding a, 0-unsaturated enones (eq 5). The reaction of 2-pyridyl-substituted vinylsilanes with bromine and subsequent treatment with sodium methoxide affords the corresponding vinyl bromides (eq 6). ... 

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