Formation of Grignard Reagents from Alkenyl Halides

by James

Description: Treatment of an alkenyl halide with magnesium metal leads to formation of the Grignard reagent. This is usually done in an ethereal solvent.
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Notes: X here is a halide. This can work with alkyl (or alkenyl) chlorides, bromides, or iodides. Sometimes “ether” is written. This is the solvent.

Examples:

Notes: Note that in example 2 the structure below the arrow is diethyl ether. This is just a solvent – it doesn’t take part in the reaction.

Mechanism: Note that the mechanism of this reaction is generally not considered important for Org 1 / Org 2. The first step here is donation of electrons to Br from the Mg. This leads to fragmentation of the C–Br bond, forming a radical. The second step is reformation of the C–Mg bond to give the Grignard reagent.

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