TS-Torquoselectivity from Global Conformational Profile

From the global conformational profile and differential activation free energies of conrotatory outward and inward ring openings of all the conformers, it is shown that (a) 3-OMe-cyclobutene must open exclusively outward and (b) conformers exist for 3-CHO- and 3-COMe-cyclobutenes that will open outwards as well. All the conformers of 3-OMe-, 3-CHO- and 3-COMe-cyclobutenes are, respectively, within 5.6, 3.2 and 4.0 kcal/mol and, hence, abundantly available under the reaction conditions. 3-OMe-cyclobutene is experimentally known to open exclusively outward. 3-CHO-cyclobutene opens > 98% inward and < 2% outward. In contrast with 3-CHO-cyclobutene, 3-COMe-cyclobutene furnishes a 3:2 mixture of the outward and inward products, respectively.