Concerted [4+2] and Stepwise [2+2]cycloadditions of the Triphenylallenyl Cation with Cyclopentadiene

stepwise and concerted cycloaddition reactions is in mechanistic chemistry. ’ Whereas stepwise processes can often be proven by lack of stereospecifity or by trapping intermediates, 2 it is generally difficult to find unequivocal evidence for concerted processes. Stepwise cycloadditions of neutral components proceed via dipolar or diradical intermediates, which can usually not be generated specifically. In ionic cycloadditions, however, possible intermediates are cations or anions, like the products and one of the cycloaddends. In these cases, an additional tool, the independent generation of the potential intermediates, is available for mechanistic studies. In this work examine the mechanism of the title reaction. we have used this tool to