Inter- and Intramolecular [2+2+2] Cycloaddition of Alkyne Triple Bonds to the Carbonyl Function of Aldehydes and Ketones Enabled by η5-Cyclopentadienylcobalt(L)(L′)

1,7-Octadiyne underwent [2+2+2] cycloaddition to acetone in the presence of eta(5)-cyclopentadienylcobalt(L)(L ') complexes to give (eta(5)-cyclopentadienyl)[(1,4,4a,8a-eta(4))-5,6,7,8-tetrahydro-3,3-dimethyl-3H-2-benzopyran]cobalt, in which the two triple bonds and the carbonyl moiety have combined to engender a 2H-pyran ring complexed to CpCo. The scope of this reaction was explored, including cocyclizations of ynals and ynones with bis(trimethylsilyl)acetylene, as well as all-intramolecular reorganizations of alpha,omega-diynals and -diynones. Two major trajectories were observed in the case of aldehydes, the (often minor) [2+2+2] pathway and a competing trail featuring a formal 1,5-hydride shift that results in CpCo-dienones. The latter is obviated for ketone substrates. Preliminary chemistry of selected complexes uncovered unprecedented reactions, such as acid-catalyzed ring openings and additions of amines, the latter providing access to novel carbon frames.

Automated summary

The article discusses the reaction products of 1,7-octadiyne with acetone under specific conditions, as well as the exploration of the reaction scope, demonstrating the different behaviors of different substrates in the reaction process.