Letter
Nickel-Catalyzed Asymmetric Hydrogenation of Cyclic Alkenyl
Sulfones, Benzo[b]thiophene 1,1-Dioxides, with Mechanistic Studies
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ABSTRACT: A highly efficient catalytic system based on the
cheap transition metal nickel for the asymmetric hydrogenation of
challenging cyclic alkenyl sulfones, 3-substituted benzo[b]-
thiophene 1,1-dioxides, was first successfully developed. A series
of hydrogenation products, chiral 2,3-dihydrobenzo[b]thiophene
1,1-dioxides, were obtained in high yields (95−99%) with excellent
enantioselectivities (90−99% ee). According to the results of
nonlinear effect studies, deuterium-labeling experiments, and DFT calculation investigations, a reasonable catalytic mechanism for
this nickel-catalyzed asymmetric hydrogenation was provided, which displayed that the two added hydrogen atoms of the
hydrogenation products could be from H2 through the insertion of Ni−H and subsequent hydrogenolysis.
symmetric hydrogenation of prochiral unsaturated
compounds has been regarded as a powerful and
desired product.9k In addition, these Ni-catalyzed asymmetric
hydrogenation reactions were mainly focused on acyclic
functionalized olefins and imines as substrates, which were
always in accordance with this catalytic mechanism. In
contrast, cyclic functionalized olefin substrates have rarely
been investigated.
A
straightforward synthetic method to access chiral compounds
that has been widely applied in the fields of agrochemicals and
pharmaceuticals.1 Most well-established asymmetric hydro-
genation methods are based on heavy noble transition metal
catalytic systems, mainly focused on ruthenium,2 iridium,3
rhodium,4 and palladium.5 However, these precious metal
catalysts could suffer from the difficulties of high costs, limited
resources, strong toxicity, and negative environmental impact.
Therefore, great attention has been devoted to the develop-
ment of cheap, sustainable, earth-abundant transition metal
catalytic systems for asymmetric hydrogenation.6 In recent
years, some iron-, cobalt-, and nickel-catalyzed asymmetric
(transfer) hydrogenation reactions of prochiral unsaturated
compounds with CC, CO, or CN bonds were
reported7−9 that demonstrated the great potential advantages
of the cheap first-row transition metals in asymmetric
hydrogenation. Among these asymmetric catalytic systems,
Ni-catalyzed asymmetric hydrogenation was relatively less
investigated. Some pioneering and important research works
on Ni-catalyzed asymmetric (transfer) hydrogenation of
prochiral ketones, alkenes, ketimines, and enamides were
developed by Hamada,9a,b Chirik,9c Zhou,9d−i Zhang,9j and our
group.9k−p In 2016, Chirik and co-workers developed the Ni-
catalyzed asymmetric hydrogenation of α,β-unsaturated esters
and performed deep research on the catalytic mechanism,
proposing conjugate addition of the Ni−H species and
nonselective protonation to release the product.9c In 2017,
our group realized Ni-catalyzed asymmetric hydrogenation of
β-acylamino nitroolefins, and experimental and DFT computa-
tional investigations revealed that it also involved 1,4-hydride
addition of Ni−H and subsequent protonation to generate the
Chiral cyclic sulfone scaffolds are widely distributed in many
biologically active compounds and natural products with
important applications.10 Because of the rigidity of cyclic
functionalized olefins, the asymmetric hydrogenation of
unsaturated cyclic sulfones to access these motifs is still in
an early stage, and just a few examples involving unsaturated
cyclic sulfones have been developed.2l,3o,p,4k In 2012,
Andersson and co-workers described Ir-catalyzed enantiose-
lective hydrogenation of prochiral cyclic and acyclic unsatu-
rated sulfones with excellent results.3o In 2017, Pfaltz and co-
workers successfully developed Ir-catalyzed asymmetric hydro-
genation of cyclic alkenyl sulfones, benzo[b]thiophene 1,1-
dioxides.3p Recently, our group realized Rh/N-methylated
bisphosphine−thiourea ZhaoPhos-catalyzed asymmetric hy-
drogenation of these cyclic alkenyl sulfones with excellent
results by the assistance of the possible hydrogen-bonding
interaction between the substrate and the ligand.4k However,
cheap transition metals have never been applied to catalyze the
asymmetric hydrogenation of cyclic alkenyl sulfones. On the
Received: November 8, 2020
Published: January 20, 2021
© 2021 American Chemical Society
Org. Lett. 2021, 23, 668−675
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