The development of a novel cooperative catalytic system for an amine–silver co-catalyzed Conia-ene reaction of alkyne-tethered C–H-acidic compounds is reported.
Lewis acidic indium(III) salts, in particular In(NTf2)(3), effect the conversion of alpha-(omega'-alkynyl)-beta-ketoesters; and omega-alkynyl-beta-ketoesters to the corresponding cyclic products in a manner known as the Coniaene reaction. This reaction can lead to the creation of five- to fifteen-membered-ring carbocycles and heterocycles in good to excellent yields. The synthetic features of the reaction are a relatively low catalyst loading, as low as 0.01 mol % in the best case, as well as no requirement of solvent for five-membered-ring formation and the requirement of only moderately dilute reaction conditions for medium-sized-ring formation. The high reactivity of indium salts is due to the double activation of the beta-ketoester substrate containing an acetylene function. The indium metal activates the beta-ketoester moiety by the formation of an indium enolate, and this indium metal electrophilically activates the alkyne moiety. Such a strong push-pull activation of the substrate by a single metal circumvents the disadvantage of entropic and enthalpic factors generally associated with the formation of medium- and large-sized rings. The reaction allows the ready formation of a fifteen-membered-ring carbocycle, from which di-muscone has been synthesized.
Ni(II)-Catalyzed Conia-Ene Reaction of 1,3-Dicarbonyl Compounds with Alkynes
作者:Qiang Gao、Bao-Fu Zheng、Jin-Heng Li、Dan Yang
DOI:10.1021/ol050532q
日期:2005.5.1
We have discovered a Ni(II)-catalyzed Conia-ene reaction of 1,3-dicarbonyl compounds with alkynes. In the presence of Ni(acac)(2) and Yb(OTf)(3), various acetylenic 1,3-dicarbonyl compounds underwent Conia-ene reaction to give mono- and bicyclic olefinic cyclopentanes. A mechanism involving the enol-yne-Ni complex formation is proposed and supported by deuterium-labeling experiments.