Denmark’s modification

It has been shown that bis(chloromethyl)zinc in 1,2-dichloroethane (Denmark s modification) is particularly effective for the cyclopropanation of iodo-substituted allylic alcohols (equation 30) . The cyclopropanation of dihalo-substituted alkenes is a lot more difficult due to the significant decrease in the nucleophilicity of the alkene, thus resulting in much lower yields of the desired products (equation. In this case, significant amounts of 0-methylation were also observed. 

The cyclopropanation of vinyl halides is also effective, with fluoro-, bromo- and iodo-substituted olefins all being suitable substrates. For example, vinyl bromide 16 underwent the reaction in good yield, using Denmark s modification of the reaction (see 1.4.5.1). ... 

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See also in sourсe #XX -- [ ]

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