Alkenes and Grignard reagents

Scheme 5.23 Tandem cyclisation/cross-coupUng reaction between alkene and Grignard reagents catalysed by a NHC-Co...

Additions occur more easily if a carbanion with resonance or inductive stabilization is formed in the addition. Thus, fulvenes are very reactive, vinylsilanes and highly fluorinated alkenes somewhat less so. Styrene, 1,3-dienes, and enynes are more reactive than isolated alkenes, and Grignard reagents may be used to initiate anionic polymerization of styrenes, dienes, and acryhc monomers. Strained alkenes such as norbomenes and cyclopropenes are also more reactive. Examples of additions facilitated by resonance or substitution are shown in Scheme 8. 

Grignard reagents add to the double bond of a cyclopropene to give a stereospecifically cis product " in a reaction that is common to strained double bonds. The reactions are first order in both alkene and Grignard reagent and the addition is relatively insensitive to steric bulk (equation 49). The kinetic data support product formation by a polar four... 

Scheme 13.14 The iron-catalysed reaction between alkenes and Grignard reagents.

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See also in sourсe #XX -- [ ]

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