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Catalytic Asymmetric Enyne Addition to Aldehydes and Rh(I)-Catalyzed Stereoselective Domino Pauson–Khand/[4 + 2] Cycloaddition

Chen, Wei, Tay, Jia-Hui, Ying, Jun, Yu, Xiao-Qi, Pu, Lin
Journal of organic chemistry 2013 v.78 no.6 pp. 2256-2265
alcohols, aldehydes, ambient temperature, carbon, catalysts, enantioselectivity, organic chemistry
The 1,1′-bi-2-naphthol–ZnEt₂–Ti(OⁱPr)₄–Cy₂NH system is found to catalyze the 1,3-enyne addition to aliphatic aldehydes as well as other aldehydes at room temperature with 75–96% yield and 82–97% ee. This system is also broadly applicable for the highly enantioselective reaction of other alkyl-, aryl-, and silylalkynes with structurally diverse aldehydes. The propargylic alcohols prepared from the catalytic asymmetric enyne addition to aliphatic aldehydes are used to prepare a series of optically active trienynes. In the presence of a catalytic amount of [RhCl(CO)₂]₂ and 1 atm of CO, the optically active trienynes undergo highly stereoselective domino Pauson–Khand/[4 + 2] cycloaddition to generate optically active multicyclic products. The Rh(I) catalyst is also found to catalyze the coupling of a diyne with CO followed by [4 + 2] cycloaddition to generate an optically active multicyclic product. These transformations are potentially useful for the asymmetric synthesis of polyquinanes containing a quaternary chiral carbon center.