Thermal reactions of benzodisilacyclobutene (1) and disilacyclobutene (2) with acetylene were investigated theoretically. The reactions are thought to proceed via the conventional Diels− Alder reaction of disilabutadiene, the conrotatory ring-opening product of disilacyclobutene, with acetylene. However, this mechanism is incompatible with the observed similar reactivities of 1 and 2 with acetylene and the retention of stereochemistry during the reaction. In our previous paper, we proposed an alternative [2 + 1] cycloaddition pathway that involved the direct addition of acetylene to the Si−Si σ−bond of 1 without ring opening. In this study, we extensively investigated the reaction pathways for both 1 and 2 on a theoretical basis. We found that charge transfer (CT) played a key role in the [2 + 1] cycloaddition pathway. On the basis of natural bond orbital (NBO) analysis, the interaction of the Si−Si σ-bond orbital (donor) with the π* orbital (acceptor) of the acetylene was attributed mainly to the CT process. Finally, an experiment to verify the [2 + 1] cycloaddition mechanism was proposed, in which the use of triacetylene as a terminal alkyne would allow the key intermediate in the pathway to be trapped.

No abstract

No abstract

No abstract