Effect of secondary MO interaction on the regiospecificity in the reactions of tf‐ionones with singlet oxygen

The ene reactions of a-ionones with singlet oxygen were examined to ascertain the effect of secondary MO interaction between the reactants on the reaction regiospecificity. Exclusive formation of 3-hydroxy-V-ionones found in the reactions reveals favorable interaction of singlet oxygen with the acyclic fl-hydrogen atom. On the other hand, no formation of 3-hydroxy-0-ionones implies that the steric requirement was not met for the bond formation between zwitterionic perepoxide with Ci-hydrogen in the process. The MMP21 and MNDO calculations indicate minus value of the secondary interaction energy for the acyclic a-hydrogen abstraction and a repulsion between the oxygen with C1-hydrogen atom. Twisting tilting of the double bond may account for favorable attack of singlet oxygen on C3. An explanation of the excellent regiospecificity was addressed and placed in proper mechanic prospective.