Alkenyl bromides Grignard compound reactions

In all these reactions, any existing configuration of any stereogenic double bond—whether it be in the alkenyl bromide or iodide or in the alkenyl Grignard compound- is completely retained. The reactions in Figure 16.10 provide good examples. 

The order of reactivity of organic halides is I > Br > Cl > F. Although organic iodides are the most reactive, they produce more Wurtz coupling products through the radical oxidative addition process. Thus, it is usually advisable to use the chlorides or bromides, except in the case of aromatic iodides and methyl iodide. 1-Alkenyl Grignard compounds are obtained by the direct reaction of magnesium and vinylic halides in THF [6], but the reaction is not completely stereospecific and the retention of the stereochemistry of haloalkenes varies from 60-90% [7]. The difficulty associated... 

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