Department of Chemistry, University of Houston, 3585 Cullen Blvd., Fleming Building 112, Houston, TX 77204-5003, USA.
Graduate School of Energy, Environment, Water and Sustainability (EEWS), Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Korea.
Molecules. 2021 Mar 14;26(6):1615. doi: 10.3390/molecules26061615.
Two key factors bear on reaction rates for the conjugate addition of alkenyl boronic acids to heteroaryl-appended enones: the proximity of inductively electron-withdrawing heteroatoms to the site of bond formation and the resonance contribution of available heteroatom lone pairs to stabilize the developing positive charge at the enone β-position. For the former, the closer the heteroatom is to the enone β-carbon, the faster the reaction. For the latter, greater resonance stabilization of the benzylic cationic charge accelerates the reaction. Thus, reaction rates are increased by the closer proximity of inductive electron-withdrawing elements, but if resonance effects are involved, then increased rates are observed with electron-donating ability. Evidence for these trends in isomeric substrates is presented, and the application of these insights has allowed for reaction conditions that provide improved reactivity with previously problematic substrates.
诱导电子吸电子杂原子与键形成位置的接近程度，以及可用杂原子孤对的共振贡献稳定烯酮 β-位上的正电荷。对于前者，杂原子离烯酮 β-碳越近，反应越快。对于后者，苄基正电荷的共振稳定作用加速了反应。因此，反应速率随着诱导电子吸电子元素的接近而增加，但是如果涉及共振效应，则观察到电子给体能力增加时反应速率增加。呈现了这些趋势在异构底物中的证据，并且这些见解的应用允许提供改进的反应条件，从而提高了之前有问题的底物的反应性。
