Singlet oxygen additions to hexacyclo[10.2.1.02,11.04,9.04,14.09,13]pentadeca-5,7-dien-3,10-diones. A remarkable substituent effect on π-face selectivity induced by transition state geometric distortions

Abstract

Face selectivity in singlet oxygen addition to a rigid polycyclic diene is reversed by sterically neutral 1,4-substitution, an effect attributed to lone pair repulsions induced by out-of-plane bending at the transition state.