ALKYLATION OF ALLYLIC DERIVATIVES .17. CROSS-COUPLING REACTIONS OF DIALLYLIC PIVALATES WITH BUTYLCOPPER AND PHENYLCOPPER REAGENTS

Cross coupling (Z)-1-phenyl-1,4-pentadien-3-yl pivalate (cis-1-OPiv) with LiCuBu2, LiCu(CN)Bu, LiCuPh2, and LiCu(CN)Ph gives only the fully conjugated gamma-coupling product. With LiCuBu2, substantial loss of double-bond configuration occurs to give primarily the all-trans coupling product. With other cuprates, no detectable loss of double-bond configuration was observed. Cross coupling (Z)-3-(2-phenylethenyl)2-cyclohexen-1-yl pivalate (cis-18-OPiv) with LiCuBu2, LiCuPh2, and LiCu(CN) ph gives only alpha-coupling product; with LiCu(CN)Bu, a mixture of alpha, gamma, and epsilon coupling product was obtained. Cross coupling with LiCuBu2, results in loss of double-bond configuration in the alpha-alkylation product. With the other cuprates, no loss of double-bond configuration was detected in the alpha and gamma coupling product. These results have profound mechanistic implications, which are discussed. The relationship between structure and reactivity was also investigated. A variety of diallylic pivalates (1-5 OPiv) were prepared and cross coupled with LiCuBu2, LiCu(CN)Bu, LiCuPh2, and LiCu(CN)Ph. Generally, coupling occurs at the least-substituted allylic system; mechanistic implications are discussed.