| Generally, the long-range electronic communication between orthogonal orbitals is inefficient and limited to field and inductive effects. We illustrate how substituent effects can be transferred between orthogonal orbitals when the energy gap between these orbitals approaches zero, or at an "orbital crossing". The crossing between two empty or two fully occupied MOs, which do not lead to stabilization, can be activated once one of the empty MOs is populated (electron injection) or once one of the filled MOs is depopulated (hole injection). In reductive cycloaromatization reactions such crossings correspond to the transition states with energies defined by both the in-plane and out-of-plane π-systems. Herein, we provide experimental evidence for the efficiency of this concept using orbital crossings in reductive C1-C5 cycloaromatization reactions of enediynes. Communication with remote substituents via orbital crossings greatly enhances regioselectivity of the ring closure step in comparison to the analogous radical cyclizations. We also present photophysical and electrochemical data pertaining to the efficiency of electron injection into the benzannelated enediynes. |
