We report a strategy for effecting catalytic, enantioselective carbocationic rearrangements through the intermediacy of alkyl iodanes as stereodefined carbocation equivalents. Asymmetric Wagner–Meerwein rearrangements of β-substituted styrenes are catalyzed by the C₂-symmetric aryl iodide 1 to provide access to enantioenriched 1,3-difluorinated molecules possessing interesting and well-defined conformational properties. Hammett and kinetic isotope effect studies, in combination with computational investigations, reveal that two different mechanisms are operative in these rearrangement reactions, with the pathway depending on the identity of the migrating group. In reactions involving alkyl-group migration, intermolecular fluoride attack is product- and enantio-determining. In contrast, reactions in which aryl rearrangement occurs proceed through an enantiodetermining intramolecular 1,2-migration prior to fluorination. The fact that both pathways are promoted by the same chiral aryl iodide catalyst with high enantioselectivity provides a compelling illustration of generality across reaction mechanisms in asymmetric catalysis.

我们报告了一种通过催化烷基碘代体作为立体定义碳正离子当量的中介来实现催化，对映选择性碳正离子重排的策略。C _2-对称的芳基碘化物1催化β取代苯乙烯的Wagner-Meerwein不对称重排提供进入富含对映体的1,3-二氟分子的途径，这些分子具有有趣且定义明确的构象性质。Hammett和动力学同位素效应研究与计算研究相结合，揭示出在这些重排反应中有两种不同的机制起作用，其途径取决于迁移群体的身份。在涉及烷基迁移的反应中，分子间氟化物的进攻是产物和对映体的决定。相反，发生芳基重排的反应通过在氟化之前对映体确定分子内1,2-迁移来进行。两种途径均由具有高对映选择性的相同手性芳基碘化物催化剂促进，这一事实为不对称催化反应机理的一般性提供了令人信服的说明。