Using Triethynylphosphine Ligands Bearing Bulky End Caps To Create a Holey Catalytic Environment: Application to Gold(I)-Catalyzed Alkyne Cyclizations
作者:Atsuko Ochida、Hideto Ito、Masaya Sawamura
DOI:10.1021/ja066800c
日期:2006.12.1
and catalytic uses of phosphinoalkynes bearing bulky end caps at the alkyne termini, that is, tris[(triarylsilyl)ethynyl]phosphines are reported. The most salient feature of the new phosphines is the holey molecular shape possessing a deep and large-scale metal-binding cavity. The holey phosphines displayed remarkable rate enhancement in the gold(I)-catalyzedsix- and seven-memberedring forming cyclizations
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.