| The reactivity of numerous aryl, alkyl, and alkenyl Group VI Fischer carbene complexes with a variety of acyclic enynes, dienynes, and trienynes has been examined. Although these reactions were found to produce a diverse array of compounds, distinct patterns were discovered which allow for the rational prediction of products based on their mechanisms of formation. In general, with chromium as the metal, insertion of carbon monoxide occurred generating such products as hydroquinones, cyclopentenones, and dienals. When carbene complexes of molybdenum were employed, the product distribution was found to be highly dependent on the alkyl substituent of the carbene complex. Aryl substituted molybdenum carbene complexes produced hexahydroazulenes, while alkenyl substituted molybdenum carbene complexes gave hydroquinones or cyclopentadiene derivatives. Application of these reactions to the synthesis of the dolabellane diterpenes is presented.; A dioxenylmolybdenum carbene complex was found to readily react with various enynes to form tetracyclic products. The tetracyclic products appear to be generated via an intramolecular Diels-Alder cycloaddition of an initially formed trialkoxycyclopentadiene derivative. Studies which help to define the generality of this reaction are reported, and the involvement of the metal in the cyclization process is discussed.; In connection with a molybdenum-mediated all-intramolecular cyclization approach to the phorbol esters, reactions to give an appropriately functionalized BC ring system of phorbol were investigated. The steric and electronic nature of the oxygen protecting groups were found to greatly effect the product distribution, with bulky, electron-withdrawing moieties promoting the desired cyclopropanation pathway. |
