Halogen Atom Participation in Guiding the Stereochemical Outcomes of Acetal Substitution Reactions
作者:Krystyna M. Demkiw、Wouter A. Remmerswaal、Thomas Hansen、Gijsbert A. van der Marel、Jeroen D. C. Codée、K. A. Woerpel
DOI:10.1002/anie.202209401
日期:2022.10.17
Nucleophilic additions to α-haloacetals proceed via an oxocarbenium ion intermediate where the carbon-halogen bond can either adopt a pseudo-axial or a pseudo-equatorial position. trans-Selectivity is typically observed when a halogen atom is positioned at C-2 of an acetal because hyperconjugative interactions involving the pseudo-axial carbon-halogen bond stabilize the oxocarbenium ion intermediate
α-卤代缩醛的亲核加成通过氧碳鎓离子中间体进行,其中碳-卤素键可以采用假轴位置或假赤道位置。当卤素原子位于缩醛的 C-2 处时,通常会观察到反式选择性,因为涉及假轴碳-卤素键的超共轭相互作用稳定了氧碳鎓离子中间体。