Regioselective Allylation of Ketenes Promoted by SmI2

Ketenes react with various allylic halides mediated by 2 equiv samarium(II) diiodide (SmI2) to the ketenes to afford allylated ketones in good yields. In the reaction with γ-substituted allylic halides, the regioselectivity is influenced by the olefinic geometry of allylic halides. By using γ-substituted (E)-allylic halides, the allylation proceeds on the less hindered site (α-position) of allylic groups predominantly and the tendency was enhanced by the addition of HMPA.