[1730-25-2] · C3H5BrMg · Isopropenylmagnesium Bromide · (MW 145.29)
(terpenoid synthesis; precursor of isopropenyl metals2)
Alternate Name: 2-(bromomagnesio)propene.
Preparative Method: reaction of 2-bromopropene with magnesium in THF.4
Handling, Storage, and Precautions: the solution of isopropenylmagnesium bromide in THF must be handled with care since it is flammable and may ignite on contact with moisture and air. It should be stored and handled in an inert atmosphere (argon or nitrogen) and measured or transferred by means of a hypodermic syringe or cannula. The solution may deteriorate with time and the reagent should be titrated3 before use.
Isopropenylmagnesium bromide reacts with various electrophiles, for example, aldehydes, ketones, esters, carboxylic acids, lactones, dialkyl oxalates, anhydrides, acid chlorides, nitriles, amides, and epoxides (eq 1).1,4,5
In the presence of copper(I) salts (1-5%) in THF, it undergoes a very efficient conjugate addition to a,b-unsaturated ketones (eq 2).6 Under the same conditions, it reacts with alkyl halides (eq 3),7 epoxides (eq 4),8 and oxetane.8
Under palladium or nickel catalysis, isopropenylmagnesium bromide reacts with vinyl (eqs 5 and 6)9,10 and aryl halides or sulfides (eqs 7 and 8)10,11 to give dienes or aryl alkenes in good yields.
2-(3-Trimethylsilyl-1-propenyl)magnesium Bromide-Copper(I) Iodide reacts with epoxides and the allylsilanes obtained can be converted to a-methylene-g-lactones (eq 9).12
In the presence of Copper(I) Iodide, the same a-substituted vinylmagnesium bromide reacts with a,b-unsaturated ketones in an annulation sequence to give methylenecyclopentanes (eq 10).13
The nickel-catalyzed cross-coupling reaction of a-substituted vinylmagnesium bromides with vinyl bromides leads to terminal 1,3-dienes (eq 11).14
Gérard Linstrumelle & Mouâd Alami
Ecole Normale Supérieure, Paris, France