Cross Coupling of Allylic Derivatives, 16. Regiochemistry of Cross Coupling the Isomeric (E,E)-3,5-Heptadien-2-yl and (E,E)-2,5-Heptadien-4-yl Pivalates with Organocopper and Grignard Reagents

Article abstract of DOI:10.1021/jo00296a037

The regiochemistry of cross coupling the isomeric (E,E)-3,5-heptadien-2-yl and (E,E)-2,5-heptadien-4-yl pivalates (1-OPiv and 2-OPiv) with organocopper and Grignard reagents has been investigated.With LiCuBu2, phenylcuprates, and Grignard reagents, the cross coupling is regioselective but not regiospecific and yields predominatly conjugated product.The starting pivalates do not rearrange under conditions for lithium cuprate cross-coupling reactions; however, 2-OPiv isomerizes to 1-OPiv in the presence of Grignard reagents (i.e. , Mg(II)).For alkylation of 1-OPiv with butylcuprates , the degree of regiospecificity (γ-alkylation) increases in the order LiCuBu2 < LiCu(CN)Bu < Bu2CuMgI < n-BuMgI / 1percent CuCN.Mechanistic implications are discussed.