Saswata Gupta
UIC
Aryne-Mediated Intramolecular Alder-Ene Reaction to Form Benzo-cyclobutenes by Overcoming a Kinetic Barrier with Steric Pressure
A rare Alder-ene reaction to form a four-membered ring is described. In this process, the unfavorable thermodynamic penalty to form a four-membered ring is compensated by the relief of the strain of the aryne intermediate. On the other hand, the high kinetic barrier for reaching the required cyclic transition state is overcome by the steric bulk of a substituent next to the ene-donor. Especially, the structural elements for internal hydrogen bonding play a crucial role not only facilitating the hexadehydro Diels-Alder reaction but also the Alder-ene reaction. Competition exper-iments and DFT calculations shows that the formation of 4-membered rings is mainly controlled by kinetic factors than thermodynamic factors in this unusual intramolecular Alder-ene reactions mediated by aryne intermediates.
A rare Alder-ene reaction to form a four-membered ring is described. In this process, the unfavorable thermodynamic penalty to form a four-membered ring is compensated by the relief of the strain of the aryne intermediate. On the other hand, the high kinetic barrier for reaching the required cyclic transition state is overcome by the steric bulk of a substituent next to the ene-donor. Especially, the structural elements for internal hydrogen bonding play a crucial role not only facilitating the hexadehydro Diels-Alder reaction but also the Alder-ene reaction. Competition exper-iments and DFT calculations shows that the formation of 4-membered rings is mainly controlled by kinetic factors than thermodynamic factors in this unusual intramolecular Alder-ene reactions mediated by aryne intermediates.