The kinetic resolution of azaflavanones has been established via RuPHOX-Ru catalyzed asymmetric hydrogenation, providing chiral azaflavanones and azaflavanols in high yields with up to >20:1 dr and 99.7% ee. The...
Chiral chromanols and their derivatives have been synthesized via a RuPHOX–Ru catalyzed asymmetric hydrogenation of chromones in high yields, >20 : 1 drs and with up to 99.9% ee. The control experiments showed that the asymmetric hydrogenation of the CC double bond occurs first followed by the reduction of the CO double bond.
Rh-catalyzed sequential asymmetric
hydrogenations of
3-amino-4-chromones
have been achieved for the first time via an unprecedented dynamic
kinetic resolution under neutral conditions, providing (S,R)-3-amino-4-chromanols in high yields (up to 98%)
with excellent enantio- and diastereoselectivities (up to 99.9% ee
and 20:1 dr). The mechanistic studies based on control experiments
and density functional theory (DFT) calculations suggest that the
dynamic kinetic resolution process for the intermediate enantiomers
generated in the first hydrogenation step proceeded via a stereomutation
(or called chiral assimilation) pathway from an undesired enantiomer
to the desired enantiomer rather than via traditional racemization
of the undesired enantiomer. The protocol can be performed on a gram
scale with a relatively low catalyst loading and offers a practical
and convenient pathway for synthesizing a series of bioactive chromanols
and their derivatives.
A synthesis of chiral tetrahydroindoles has been developed via a Pd‐catalyzed asymmetric allylic substitution annulation using unstable enolizable ketimines as nucleophiles and our previously developed tBu‐RuPHOX as a chiral ligand. The reaction proceeds via an asymmetric desymmetrization of the meso‐diacetatecycloalkenes, providing the desired chiral tetrahydroindoles in moderate to good yields and with up to 96% ee. The annulation reaction could be performed on a gram‐scale in high yields and the resulting products can be transformed to several types of N‐hetereobicyclic derivatives. In addition, a chiral cis‐perhydroindolic acid derivative was also readily synthesized starting from a prepared chiral tetrahydroindole.magnified image
The efficient RuPHOX-Ru catalyzed asymmetric hydrogenation of α-substituted tetralones via a dynamic kinetic resolution has been achieved for the synthesis of chiral tetrahydronaphthols. The mechanism study indicated that the hydrogenation...
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