W (C0) ₅ (L) -Catalyzed Construction of Cyclic Carbon Frameworks

Abstract

Several novel reactions are developed utilizing the electron-deficient nature of terminal alkyne-W (CO) ₅ π-complexes and/or their isomerized vinylidene complexes. Terminal alkynes having a silyl enol ether moiety in the molecule undergo endo-selective cyclization using a catalytic amount of W (CO) ₅ (thf). In some cases, both exo-and endo-selective cyclizations are achieved depending on the reaction conditions. Iodinated vinylidene intermediates are generated from the corresponding iodoalkynes and W (CO) ₅ (thf), and are employed for the related cyclizations. Electrocyclization of o-ethynylphenyl ketones gives novel benzopyranylidene complexes, which undergo Diels-Alder reaction with electron-rich alkenes to give substituted naphthalenes. Furthermore, the reaction of o-ethynylphenyl ketones and electron-rich alkenes in the presence of a catalytic amount of W (CO) ₅ (thf) proceeds through the novel tungsten-containing carbonyl ylides, which react with the electron-rich alkenes in a [3+2] -cycloaddition manner to give polycyclic compounds.