Structure and reactivity of vinylcyclopropane radical cation: Electron transfer photochemistry and ab initio calculations

The electron-transfer photochemistry of vinylcyclopropane (1) generates three ring-opened products, 2-4, each bearing a methoxy as well as a 4- cyanophenyl group. The products are ascribed to nucleophilic attack of methanol on the radical cation, 1·+^. The attack is regioselective but not regiospecific; attack at the secondary cyclopropane carbons, leading to 2 and trans-3, is preferred; attack at the terminal vinylic carbon, yielding trans- 4, occurs to a lesser extent. The potential surface of 1·⁺ was probed by ab initio calculations; 1·⁺ has two minima, anti- and syn-1·⁺; both have C(s) symmetry and belong to the unusual structure type with two lengthened cyclopropane bonds. The calculations are in general agreement with the observed reaction pattern.