Isotope Effects and Mechanism of the Asymmetric BOROX Brønsted Acid Catalyzed Aziridination Reaction

The mechanism of the chiral VANOL-BOROX
Brønsted acid catalyzed
aziridination reaction of imines and ethyldiazoacetate has been studied
using a combination of experimental kinetic isotope effects and theoretical
calculations. A stepwise mechanism where reversible formation of a
diazonium ion intermediate precedes rate-limiting ring closure to
form the cis-aziridine is implicated. A revised model
for the origin of enantio- and diastereoselectivity
is proposed based on relative energies of the ring-closing transition
structures.

本研究结合实验动力学同位素效应（kinetic isotope effects）与理论计算手段，针对手性VANOL-BOROX布朗斯特酸（Brønsted acid）催化亚胺与重氮乙酸乙酯发生氮丙啶化反应的机理展开了系统探究。结果表明，该反应遵循分步机理：重氮鎓离子中间体的可逆生成先于限速环闭合步骤，最终生成顺式氮丙啶。基于环闭合过渡态结构的相对能量，本研究提出了用于阐释该反应对映选择性与非对映选择性起源的修正模型。