Stereoselective Nickel-Catalyzed [2+2+2] Cycloadditions and Alkenylative Cyclizations of Ene-Allenes and Alkenes

摘要

Transformations that facilitate the rapid generation of molecular complexity in the form of carbocyclic and heterocyclic structures are invaluable in organic synthesis. Such reactions enable highly step-economical or "greener" synthetic approaches to complex molecules from simple substrates. Transition-metal-catalyzed multicomponent [m+n+o]-type cycloadditions are prototypical examples of this type of process. Variants using multiple alkynes have been particularly successful, exemplified by the alkyne cyclotrimerization reaction for constructing benzenoid systems. There are few intermolecular multicomponent cycloadditions reported using multiple alkenes, however. In 1999, Montgomery disclosed a nickel-catalyzed intermolecular [2+2+2] cycloaddition of two enones and one alkyne for the synthesis of substituted hydrindanes [Eq. (1); cod = cyclooctadienyl] . Very recently, Tanaka has reported the first enantioselective [2+2+2] cycloaddition involving two alkenes and one alkyne using cationic rhodium catalysis, although this reaction is strictly limited to monosubstituted or 1,1-disubstituted alkenes and uses acrylamides as the sole added πcomponent [Eq. (2)]