Axially chiral enamides bearing a N-C axis have been recently studied and were proposed to be valuable chiral building blocks, but a stereoselective synthesis has not been achieved. Here, we...
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.
All-carbon quaternary stereocenters
are versatile building blocks,
and their asymmetric construction has attracted much attention. Herein,
we disclose an axial-to-central chirality transfer strategy for the
synthesis of chiral quaternary stereocenters via dearomatization of
(S)-BINOLs. The reaction proceeded smoothly with
a wide range of propargyl carbonates to afford chiral spiro-compounds in high yields with excellent enantioselectivities. In
addition, the strategy was extended to kinetic resolution of rac-BINOLs albeit with moderate s value.
An
efficient tandem cycloisomerization–amination reaction
catalyzed by silver is described. This rapid and atom-economic reaction
delivered 1-amino-2H-quinolizin-2-one scaffolds in
high yields under mild conditions. The reaction could be extended
to an asymmetric version albeit with moderate enantioselective excess
of the products. In addition, the products can be easily reduced into
various azabicycles containing 4-pyridones, which are important building
blocks in organic synthesis.
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