1430348-08-5Relevant academic research and scientific papers
Orbital Crossings Activated through Electron Injection: Opening Communication between Orthogonal Orbitals in Anionic C1-C5 Cyclizations of Enediynes
Peterson, Paul W.,Shevchenko, Nikolay,Breiner, Boris,Manoharan, Mariappan,Lufti, Forat,Delaune, Jess,Kingsley, Margaret,Kovnir, Kirill,Alabugin, Igor V.
supporting information, p. 15617 - 15628 (2016/12/16)
Generally, the long-range electronic communication between spatially orthogonal orbitals is inefficient and limited to field and inductive effects. In this work, we provide experimental evidence that such communication can be achieved via intramolecular electron transfer between two degenerate and mutually orthogonal frontier molecular orbitals (MOs) at the transition state. Interaction between orthogonal orbitals is amplified 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” when one of the empty MOs is populated (i.e., electron injection) or one of the filled MOs is depopulated (i.e., hole injection). In reductive cycloaromatization reactions, such crossings define transition states with energies defined by both the in-plane and out-of-plane π-systems. Herein, we provide experimental evidence for the utility 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 data pertaining to the efficiency of electron injection into the benzannelated enediynes.
stereoelectronic umpolung : Converting a p-donor into a σ-acceptor via electron injection and a conformational change
Peterson, Paul W.,Shevchenko, Nikolay,Alabugin, Igor V.
supporting information, p. 2238 - 2241 (2013/06/27)
The para-OMe functional group, usually regarded as a conjugative p-donor, acts as an efficient hyperconjugative σ-acceptor in reductive cycloaromatization reactions. This apparent reversal of electronic properties is associated with a conformational change that aligns the σO-C orbital with the adjacent aromatic system and provides stabilization to the developing negative charge in the TS of the dianionic cyclization of enediynes. The chameleonic character of the OMe group illustrates the important role of negative hyperconjugation in anionic processes.
