New General Method for Regio- and Stereoselective Allylic Substitution with Aryl and Alkenyl Coppers Derived from Grignard Reagents

Allylic substitution with Sp(2)-carbon reagents (aryl and alkenyl anions) was realized by using allylic picolinates and copper reagents derived from RMgBr and CuBr center dot Me2S to afford anti S(N)2' products regio- and stereoselectively. Steric and electronic factors in the reagents and the size of the methylene substituents around the allylic moiety marginally affected the selectivity. The reaction system was compatible with alkyl reagents as well. Furthermore, the substitution was applied to construction of a quaternary center and synthesis of (-)-sesquichamaenol. Electron-withdrawing nature of the pyridyl group and chelation of the C(=O)-C5H4N to MgBr2 generated in situ were found to be responsible for the high efficiency of the substitution.