Cu(I)-Catalyzed Enantioselective [2 + 2] Cycloaddition of 1-Methoxyallenylsilane with α-Imino Ester: Chiral Synthesis of α,β-Unsaturated Acylsilanes

[reaction: see text] The catalytic, enantioselective [2 + 2] cycloaddition reaction of 1-methoxyallenylsilanes with alpha-imino ester has been achieved by means of the [Cu(MeCN)(4)]BF(4)/(R)-Tol-BINAP catalyst to afford 3-methylene-azetidine 2-carboxylates in good yields and with excellent enantiomeric excesses. The acid-catalyzed ring opening of the azetidines afforded chiral acylsilanes quantitatively.