Construction of Carbon Frameworks by the Catalytic Use of Low-Valent Carbonyl Complexes of Group 6 Metals

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A novel W(CO)ィイD25ィエD2-catalyzed endo selective cyclization of ω-acetylenic silyl enol ethers was developed. It was expected that treatment of ω-acetylenic silyl enol ethers with W(CO)ィイD25ィエD2・THF would generate electrophilic alkyne-W(CO)ィイD25ィエD2 complexes and/or their isomerized vinylidene complexes and that intramolecular attack of the silyl enol ether part on the tungsten-coordinated alkyne would occur to give cyclized product. In practice, the reaction proceeded as expected and endo cyclized product was obtained selectively in most cases with a catalytic amount of the complex. Furthermore, even in the case of the reaction where exo cyclization was favored under the similar reaction conditions, endo product was obtained as a major product by choosing appropriate reaction conditions. This reaction was further expanded to the annulation of five- or six-membered ring onto α,β-unsaturatred ketones by the combination of 1,4-addition of propargylmalonate with trapping the produced enolates as silyl enol ethers, followed by the W(CO)ィイD25ィエD2-catalyzed cyclization.By treatment of benzenes ortho-substituted with an alkenyl group and a terminal acetylene with 5 mol% amount of W(CO)ィイD25ィエD2・THF, 6π-electrocyclization proceeded via tungsten vinylidene intermediates to give naphthalene derivatives in high yields. This reaction was further applied to the facile synthesis of various hetero-polyaromatics.