Closer Investigation of the Kinetics and Mechanism of Spirovinylcyclopropyl Oxindole Reaction with Σg-O by Topological Approaches and Unraveling the Role of the I Catalyst.

In this investigation at the MN15L/Def2-TZVP level of theory, we present computational evidence indicating that the reaction of Σg-O with spirovinylcyclopropyl oxindole () leads to a product called spiro-1,2-dioxolane () in its singlet state; this reaction occurs via a stepwise mechanism and its rate-determining step is catalyzed by iodine radicals, which promotes opening of the three-membered ring under dark conditions. The conversion of to 1-benzylindoline-2,3-dione () and 2-vinyloxirane () takes place via a concerted and slightly asynchronous reaction. Both electron localization function and AIM topological analysis reveal that the step associated with the attack of the Σg-O molecule on the intermediate characterizes the formation of the only new O-C single bond, which occurs in a stepwise mechanism, in contrast to the Δg-O reaction with species.