A Chiral N, N′‐Dioxide–ZnII Complex Catalyzes the Enantioselective [2+2] Cycloaddition of Alkynones with Cyclic Enol Silyl Ethers. Issue 18 (5th April 2016) - Kang, Tengfei
Abstract: A highly efficient enantioselective [2+2] cycloaddition between alkynones and cyclic enol silyl ethers was developed by using a chiral N, N′ ‐dioxide‐zinc(II) complex as a catalyst. This method functions well for a variety of terminal alkynes as well as cyclic enol silyl ethers, with good to excellent enantioselectivity (up to 97 % ee ). This is also the first successful example for the catalytic enantioselective [2+2] cycloaddition of internal alkynes with cyclic enol silyl ethers to give fully substituted cyclobutenes. Meanwhile, the desired cyclobutene product can easily be transformed into fused cyclobutane derivatives. Abstract : Fused cyclobutenes : The title reaction was realized by using a chiral N, N′ ‐dioxide–Zn(NTf2 )2 catalyst. The reaction functions well for a variety of terminal alkynes and cyclic enol silyl ethers, providing good to excellent enantioselectivity. Internal alkynes were utilized in this reaction to give fully substituted cyclobutenes. TBS= tert ‐butyldimethylsilyl.