Development of Novel Synthetic Reactions Utilizing Transition-Metal Complexes Containing Carbon-Metal Multiple Bonds

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This research has focused on the development of novel carbon-carbon bond forming reactions utilizing the transition metal complexes containing carbon-metal multiple bonds.1) Two types of novel reactive species were generated by one-electron reduction of Fischer-type carbene complexes. In the case of tungsten complexes, one-electron reduction generated anion radical species, which added to electron-deficient olefins to give addition products. In the case of chromium complexes, carbonyl insertion occurred to give acyl chromate complexes, which underwent 1, 4-addition to various electron-deficient olefins.2) Treatment of o-ethynylphenylketone derivatives with W(CO_5・THF gave novel benzopyranylidene complexes through electrocyclization of vinylidene intermediates. These complexes readily underwent inverse electron demand Diels-Alder reaction with electron-rich olefins to give naphthalene derivatives in good yield. Furthermore, we have developed a novel method for the generation of metal-containing carbonyl ylides by the reaction of o-ethynylphenyl ketones with W(CO)_5・THF. The [3+2]-cycloaddition of these ylides with electron-rich alkenes followed by insertion of the resulting tungsten carbene moiety into a neighboring C-H bond realizes the construction of complex cyclic carbon frameworks in a single step. This reaction was further developed into a novel method for the synthesis of polycyclic indole derivatives through the generation of metal-containing azomethine ylides.3) Treatment of ω-acetylenic silyl enol ethers with a catalytic amount of W(CO)_5・L realizes an effective electrophilic activation of the acetylenic moiety for the attack of the silyl enol ether part to give cyclized products in high yield. This reaction has been studied extensively and a variety of synthetically useful reactions have been developed.