W(CO)_5(L)-Catalyzed Construction of Cyclic Carbon Frameworks

摘要

Several novel reactions are developed utilizing the electron-deficient nature of terminal alkyne-W(CO)_5 pi-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. Electrocylization 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.