1-Alkenylmagnesium halides, addition

Table 2. Homoallylic Alcohols by Addition of Alkenylmagnesium Halides to Carbonyl Compounds... 

One particular example of carbometallation of alkenes is the addition of 2-alkenylmagnesium halides and bis(2-alkenyl)zinc to ethylene under pressure (20-100 bar) to give the corresponding 4-alkenylmetal compounds [95] (Scheme 7-84). 

Many simple alkyl, aryl, and 1-alkenylmagnesium compounds are readily prepared by the slow addition of organic halides to a stirred suspension of a slight excess of magnesium turnings in an ether solvent (eq. (1)). 

In general, non-catalyzed hydrometalation reactions including hydroboration proceed in a sy -fashion. When internal alkynes undergo hydrometalation followed by hydrolysis, disubstituted Z-alkenes can be accessed selectively representative examples of Ti-catalyzed hydroalumination and hydromagnesation are demonstrated in Fig. 15. In the first example, it was noted that the hydroalumination reaction in the absence of the Ti catalyst led to the -isomer [37], In the second example, it was shown that, in addition to hydrolysis, the alkenylmagnesium intermediate could undergo addition to aldehydes and alkyl halides to yield trisubstimted alkene products in high stereoselectivity [38]. 

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