SN2′ selective alkylation of allylic chlorides and mesylates with RZnX reagents generated from Grignard reagents, zinc chloride, lithium chloride, and Cu(II)-salts

Treatment of RMgX (1 equiv. R = alkyl; X = Cl, Br) with ZnCl 2 (1 equiv.) in a mixed solvent of THF and Et 2 O leads to a highly turbid white suspension. Addition of LiCl (1∼2 equiv.) solubilizes the insoluble species to yield a colorless clear solution. Addition of a catalytic amount of a Cu(II)-salt followed by allylic halides or mesylates at 0 °C ∼ room temperature yielded S N 2′products in high yields. Application for the synthesis of ( E )-alkene dipeptide isosteres is also reported.