Cobalt-catalyzed reactions of haloalkanes with dimethylphenylsilylmethylmagnesium chloride result in highly regioselective dehydrohalogenation. The reaction does not follow the conventional E2 elimination mechanism but includes beta-hydride elimination from the corresponding alkylcobalt intermediate. The interesting reaction mechanism of the cobalt-catalyzed dehydrohalogenation offered unique transformations that are otherwise difficult to attain.