posted on 2021-07-06, 22:43authored byJie Wang, Xiaotian Qi, Xiao-Long Min, Wenbin Yi, Peng Liu, Ying He
Axially
chiral styrenes are of great interest since they may serve
as a class of novel chiral ligands in asymmetric synthesis. However,
only recently have strategies been developed for their enantioselective
preparation. Thus, the development of novel and efficient methodologies
is highly desirable. Herein, we reported the first tandem iridium
catalysis as a general strategy for the synthesis of axially chiral
styrenes enabled by Asymmetric Allylic Substitution-Isomerization (AASI) using cinnamyl carbonate analogues as electrophiles
and naphthols as nucleophiles. In this approach, axially chiral styrenes
were generated through two independent iridium-catalytic cycles: iridium-catalyzed
asymmetric allylic substitution and in situ isomerization
via stereospecific 1,3-hydride transfer catalyzed by the same iridium
catalyst. Both experimental and computational studies demonstrated
that the isomerization proceeded by iridium-catalyzed benzylic C–H
bond oxidative addition, followed by terminal C–H reductive
elimination. Amid the central-to-axial chirality transfer, the hydroxyl
of naphthol plays a crucial role in ensuring the stereospecificity
by coordinating with the Ir(I) center. The process accommodated broad
functional group compatibility. The products were generated in excellent
yields with excellent to high enantioselectivities, which could be
transformed to various axially chiral molecules.