Lewis Acid Mediated Reactions of Organocopper Reagents. A Remarkably Enhanced Regioselective γ-Attack of Allylic Halides and Direct Alkylation of Allylic Alcohols via RCu*BF3 System

Article abstract of DOI:10.1021/ja00527a032

Chemical reactivities and selectivities of a new class of organocopper reagent, RCu-Lewis acid, are described.Regioselective γ-attack of allylic halides is realised irrespective of the degree of substitution at the two ends of the allylic systems, and of the structural factors (cyclic or acyclic) involved.Among the Lewis acids examined, BF3*OEt2 is the most effective with respect to the selectivity and total yield.Propargyl chloride and acetate are converted into 1,2-heptadiene by n-BuCu*BF3.Allylic alcohols react with 3 equiv of RCu*BF3 to produce the corresponding alkylation products in high yield.The stereochemistry of the reactions of RCu*BF3 is examined by using Goering's system, that is, 5-methyl-2-cyclohexenyl chloride, acetate, and alcohol.The substitution proceeds through a formal anti S_N2' in the case of cis-5-methyl-2-cyclohexenyl acetate and through a formal syn S_N2' in trans-5-methyl-2-cyclohexen-1-ol.On the other hand, the stereochemical integrity dissapears in the reaction of the cis-5-methyl-2-cyclohexen-1-ol and the chloride (1).It is proposed that the "ate" complex between RCu and BF3 is involved as a reactive intermediate.