Bromination-desilicobromination

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. " ... 

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