Reactions of organocopper reagents involve species containing copper-carbon bonds acting as nucleophiles in the presence of organic electrophiles.
Organocopper reagents are now commonly used in organic synthesis as mild, selective nucleophiles for substitution and conjugate addition reactions.
[11] In the original paper describing this reaction, methylmagnesium bromide is reacted with isophorone with and without 1 mole percent of added copper(I) chloride (see figure).
[13] (3)More recently, catalytic enantioselective methods have been developed based on the copper(I)-catalyzed conjugate addition of Grignard reactions to enones.
The proposed mechanism involves transmetalation from the Grignard reagent to copper, conjugate addition, and rate-determining reductive elimination (see the analogous upper pathway in equation (2)).
[17] (7)Alkenylcopper complexes, easily generated through carbocupration, are useful for the introduction of a vinyl group in the β position of a carbonyl compound.
Vinyl ether cuprates serve as convenient acyl anion equivalents in conjugate addition reactions to enones.
Although magnesium bromide generated in situ from the reaction of Grignard reagents and copper(I) halides can serve this role (see above), external Lewis acids are also useful.
In the presence of boron trifluoride etherate, organocopper complexes are able to add to sterically congested enones in moderate yield (effecting the same transformation with an organocuprate would be difficult).
Because the stereoselectivity of carbocupration is extremely high, the reaction has been applied to the synthesis of pheromones in which the geometric purity of double bonds is critical.