Significant advances have been achieved
for the construction of
chiral skeletons containing 1,2,3-triazoles via transition-metal-catalyzed
asymmetric azide–alkyne cycloaddition; however, most of them
have been limited to terminal alkynes in the synthesis of central
chirality via desymmetrization and dynamic/dynamic kinetic resolution.
Enantioselective transition-metal-catalyzed azide-internal-alkyne
cycloaddition is extremely limited. Moreover, the construction of
a challenging five-membered (hetero)biaryl axially chiral molecule
via transition-metal-catalyzed asymmetric azide-internal-alkyne cycloaddition
is still underexplored. Herein, we first report an atroposelective
and atom-economical synthesis of axially chiral 1,4,5-trisubstituted
1,2,3-triazoles, directly acting as core chiral units of challenging
five-membered atropisomers, via the enantioselective Rh-catalyzed
azide–alkyne cycloaddition (E-RhAAC) of internal alkynes and
azides. The reaction demonstrates excellent functional group tolerance,
forging a variety of C–C axially chiral 1,2,3-triazoles under
mild conditions with moderate to excellent yields (up to 99% yield)
and generally high to excellent enantioselectivities (up to 99% ee)
along with specific regiocontrol. The origin of regio- and enantioselectivity
control is disclosed by density functional theory (DFT) calculations,
providing new guidance for the facile construction of axially chiral
compounds.
Dimethylsulfinyl anions derived from CsOH–DMSO catalyzed nitrile hydration reactions in water to give the versatile amides via interesting DMSO-participating mechanisms.
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