| Fischer carbene complexes, of all three group 6 metals, bearing siloxy-tethered enol ethers and dienol ethers undergo rapid intramolecular cyclopropanation at ambient temperatures producing 1,2-dioxygenated siloxycyclopropanes in excellent yields with absolute regio- and diastereospecificity. Dimethylsiloxy-1,3-dienol ethers cyclopropanate with alkenyl carbene complexes to give divinylcyclopropanes, which undergo tandem Cope rearrangements to produce 1,3-cycloheptadiones diastereospecifically in 60-70% yields. Allyldimethylsiloxy Fischer carbene complexes also undergo intramolecular cyclopropanation to give the silyloxycyclopropanes in excellent yield.; Siloxy Fischer carbene complexes of chromium undergo photochemical ketene formation and subsequent intramolecular (2{dollar}+{dollar}2) cycloaddition with silicon tethered allylic alcohols to generate bicyclic siloxycyclobutanones in good yield with modest diastereoselectivity, The reaction is tolerant of a broad range of alkyl and aryl substituents at the carbene carbon and a variety of allylic alcohol derivatives, providing a route to highly functionalized cyclobutanones.; An application of the chromium Fischer carbene complex intramolecular benzannulation is demonstrated in synthetic studies of (d)-Thysanone, a naphthoquinone-lactoI, which was shown to be an effective inhibitor of the human rhinovirus 3c-protease. The key benzannulation step provides a general method for regiospecific alkyne addition in cases for which the requisite alkynes offer little sterically induced regioselectivity during intermolecular benzannulation.; Aryl Fischer carbene complexes of manganese bearing a Ti(IV) substituent, (MeCp)/(CO){dollar}sb2{dollar}MnC(Ar)(OTiCp{dollar}sb2{dollar}Cl), undergo benzannulation reactions with l-hexyne under mild photochemical thermal conditions to afford naphthoquinones. The analogous manganese alkoxycarbene complexes are unreactive. Aryl siloxy Fischer carbene complexes of manganese bearing tethered acetylenic alcohols undergo intramolecular, photochemical, regiospecific benzannulation under mild conditions to exclusively excellent yields of naphthoquinones. Yields are increased in the presence of the recoverable additive diphenylacetylene. These results comprise the first efficient benzannulation process involving group 7 Fischer carbene complexes. |
