Abstract
Triplet carbenes are divalent carbon compounds and highly reactive species. Recently, Tomioka et al. reported a triplet carbene which survived nearly two
weeks in deggased benzene at room temperature. However, the carbene still reacts with oxygen and hydrogen donor solvents because kinetic stabilization around the carbonic center is still insufficient. In order to overcome these shortcomings, we designed as precursors novel allenic compounds which bear two acridinium ligands. We assumed that the formation of the carbenes could be achieved by two-electron oxidation of these allenic precursors. The oxidation of allene compound which does not bear peri substituents on the aromatic backbone afforded the dimer species in 6%. This result suggested the intermediacy of triplet carbenes. Although computational studies indicated that two-electron oxidation of the allene compounds bearing acridene skeletons would generate triplet carbenes as the ground state species, we have not been able to isolate them. Synthesis of the allenic precursors bearing steric protecting groups and the oxidation reactions will also be discussed.
