Alkenes alkylzincation

Alkynes react with indium reagents such as (allyl)3ln2l3 to form dienes (allyl substituted alkenes from the alkyne). Allyltin reagents add to alkynes in a similar manner in the presence of ZrCU Alkylzinc reagents add to alkynes to give substituted alkenes in the presence of a palladium catalyst. ... 

A unique nickel-catalyzed alkylative monofunctionalization of cyclic anhydrides using dialkylzinc and diphenylzinc provided 7- or f3-keto acids (Scheme 124).323 This reaction also required the use of Ni(cod)2 or Ni(acac)2 and a bidentate ligand. As it was observed by Knochel in the reactions of dialkylzinc with alkyl iodides (vide infra), addition of an electron-deficient alkene,324 for example, 4-fluoromethylstyrene, accelerated the rate of the reaction and increased the yield of the desired products. The alkylzinc reagents BuZnBr and Et02CCH2CH2ZnBr also reacted with anhydrides, although the yields were lower. 

Arylzinc reagents are completely inert towards alkenes and alkynes in the absence of any added catalyst, whereas the reported examples of uncatalyzed intermolecular carbozincations involving alkylzincs appear to be restricted to the more nucleophilic di(tert-butyl)zinc. 

Regio- and stereoselective synthesis of tri- and tetrasubstituted alkenes by introduction of CO2 and alkylzinc reagents into alkynes in preparation of natural products 07EJO4981. 

A modified version of the Simmons-Smith reaction uses dibromomethane and in situ generation of the Cu-Zn couple. Sonication is used in this procedure to promote reaction at the metal surface. Cyclopropanation can also be affected with a combination of CH2I2 and an alkylzinc reagent. The reaction is stereospecific and strongly regioselective. Thus, it has been found that cyclopentenol gives only the mdo-bicyclic alcohol (Scheme 5.34). The mechanism of the Simmons-Smith reaction appears to be carbene transfer from the metal to the alkene without any free carbene being released (Scheme 5.35). 

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