Chiral polyfluoroarene derivatives are an important scaffold in chemistry. An unprecedented enantioselective C−H alkylation of polyfluoroarenes with alkenes is described. The reaction employs bulky ...chiral N‐heterocyclic carbene (NHC) ligands for nickel catalysts to enable exclusive activation of C−H bonds over C−F bonds and complete endo‐selective C−H annulation and excellent enantioselectivity. A wide variety of chiral fluorotetralins, compounds otherwise difficultly accessed but serve as important bioisosteric analogs of both tetralin and heterocycle units for drug design, are expediently synthesized from easily available substrates. To our knowledge, this is the first example of catalytic enantioselective C−H functionalization of polyfluoroarenes.
The first enantioselective catalytic C−H functionalization of polyfluoroarenes is reported. This unprecedented asymmetric C−H alkylation of fluoroarenes with alkenes is enabled by using a Ni/NHC catalysis, to furnish chiral fluorotetralins in high efficiency and excellent levels of chemo‐, regio‐, and enantiocontrol.
Axially chiral biaryl scaffolds are essential structural units in chemistry. The asymmetric Pd-catalyzed Suzuki–Miyaura cross-coupling reaction has been widely recognized as one of the most practical ...methods for constructing atropisomers of biaryls. However, longstanding challenges remain in this field. For example, substrate scope is often narrow and specialized, functional groups and heterocycles can lead to reduced reactivity and selectivity, bulky ortho-substituents are usually needed, and reported methods are generally inapplicable to tetra-ortho-substituted biaryls. We have developed an unprecedented highly enantioselective N-heterocyclic carbene (NHC)-Pd catalyzed Suzuki–Miyaura cross-coupling reaction for the synthesis of atropisomeric biaryls. These reactions enable efficient coupling of aryl halides (Br, Cl) or aryl triflates with various types of aryl boron compounds (B(OH)2, Bpin, Bneo, BF3K), tolerate a remarkably broad scope of functional groups and heterocycles (>41 examples), employ low loading of catalyst (0.2–2 mol %), and proceed under mild conditions. The protocol provided general and efficient access to various atropisomeric biaryls and heterobiaryls in excellent enantioselectivities (up to 99% ee) with no need of using bulky ortho-substituted substrates and was effective for the synthesis of tetra-ortho-substituent biaryls. Moreover, the method was successfully applied to the diastereo- and enantioselective synthesis of atropisomeric ternaphthalenes. Critical to the success of the reaction is the development and application of an extremely bulky C 2-symmetric chiral NHC, (R,R,R,R)-DTB-SIPE, as the ligand for palladium. To the best of our knowledge, this is the first highly enantioselective (>90% ee) example of a chiral NHC-metal-catalyzed C(sp2)–C(sp2) cross-coupling reaction.
Catalytic assembly of enantiopure aliphatic amines from abundant and readily available precursors has long been recognized as a paramount challenge in synthetic chemistry. Here, we describe a mild ...and general copper-catalyzed hydroamination that effectively converts unactivated internal olefins—an important yet unexploited class of abundant feedstock chemicals—into highly enantioenriched α-branched amines (≥96% enantiomeric excess) featuring two minimally differentiated aliphatic substituents. This method provides a powerful means to access a broad range of advanced, highly functionalized enantioenriched amines of interest in pharmaceutical research and other areas.
A general, efficient, highly enantio‐ and chemoselective N‐heterocyclic carbene (NHC)/Ni‐catalyzed addition of readily available and stable arylboronic esters to ketones is reported. This protocol ...provides unexpectedly fast access (usually 10 min) to various chiral tertiary alcohols with exceptionally broad substrate scope and excellent functional group tolerance (76 examples, up to 98 % ee). This process is orthogonal to other known Ni‐mediated Suzuki–Miyaura couplings, as it tolerates aryl chlorides, fluorides, ethers, esters, amides, nitriles, and alkyl chlorides. The reaction is applied to late‐stage modifications of various densely functionalized medicinally relevant molecules. Preliminary mechanistic studies suggest that a rare enantioselective η2‐coordinating activation of ketone carbonyls is involved. This cross‐coupling‐like mechanism is expected to enable other challenging transformations of ketones.
A method for general asymmetric addition of arylborons to simple ketones is reported, which is enabled by nickel/N‐heterocyclic carbene catalysis. Chiral tertiary alcohols are furnished with high efficiency and excellent levels of enantio‐ and chemocontrol, and the method offers a broad substrate scope.
The development of selective reactions that utilize easily available and abundant precursors for the efficient synthesis of amines is a long-standing goal of chemical research. Despite the centrality ...of amines in a number of important research areas, including medicinal chemistry, total synthesis and materials science, a general, selective and step-efficient synthesis of amines is still needed. Here, we describe a set of mild catalytic conditions utilizing a single copper-based catalyst that enables the direct preparation of three distinct and important amine classes (enamines, α-chiral branched alkylamines and linear alkylamines) from readily available alkyne starting materials with high levels of chemo-, regio- and stereoselectivity. This methodology was applied to the asymmetric synthesis of rivastigmine and the formal synthesis of several other pharmaceutical agents, including duloxetine, atomoxetine, fluoxetine and tolterodine.
The discovery of two‐dimensional (2D) materials with unique electronic, superior optoelectronic, or intrinsic magnetic order has triggered worldwide interest in the fields of material science, ...condensed matter physics, and device physics. Vertically stacking 2D materials with distinct electronic and optical as well as magnetic properties enables the creation of a large variety of van der Waals heterostructures. The diverse properties of the vertical heterostructures open unprecedented opportunities for various kinds of device applications, e.g., vertical field‐effect transistors, ultrasensitive infrared photodetectors, spin‐filtering devices, and so on, which are inaccessible in conventional material heterostructures. Here, the current status of vertical heterostructure device applications in vertical transistors, infrared photodetectors, and spintronic memory/transistors is reviewed. The relevant challenges for achieving high‐performance devices are presented. An outlook into the future development of vertical heterostructure devices with integrated electronic and optoelectronic as well as spintronic functionalities is also provided.
The diverse properties of van der Waals heterostructures open unprecedented opportunities for various types of device applications inaccessible in conventional heterostructure materials. Research progress of vertical heterostructure device applications in vertical transistors, infrared photodetectors, and spintronic devices is reviewed, together with a discussion on the challenges and opportunities in the future development of multifunctional devices.
The transition‐metal‐catalyzed C−N cross‐coupling has revolutionized the construction of amines. Despite the innovations of multiple generations of ligands to modulate the reactivity of the metal ...center, ligands for the low‐temperature enantioselective amination of aryl halides remain a coveted target of catalyst engineering. Designs that promote one elementary reaction often create bottlenecks at other steps. We here report an unprecedented low‐temperature (as low as −50 °C), enantioselective Ni‐catalyzed C−N cross‐coupling of aryl chlorides with sterically hindered secondary amines via a kinetic resolution process (s factor up to >300). A bulky yet flexible chiral N‐heterocyclic carbene (NHC) ligand is leveraged to drive both oxidative addition and reductive elimination with low barriers and control the enantioselectivity. Computational studies indicate that the rotations of multiple σ‐bonds on the C2‐symmetric chiral ligand adapt to the changing needs of catalytic processes. We expect this design would be widely applicable to diverse transition states to achieve other challenging metal‐catalyzed asymmetric cross‐coupling reactions.
An unprecedented low‐temperature, asymmetric Ni‐catalyzed C−N cross‐coupling of sterically hindered secondary amines with aryl chlorides via kinetic resolution is reported. A bulky yet flexible, chiral NHC ligand enables both low barrier oxidative addition and reductive elimination and high levels of enantiocontrol. Computational studies indicate that multiple σ‐bond rotations of the C2‐symmetric chiral NHC adapt to the changing needs of catalytic processes.
Reported is a highly enantioselective copper‐catalyzed Markovnikov protoboration of unactivated terminal alkenes. A variety of simple and abundant feedstock α‐olefins bearing a diverse array of ...functional groups and heterocyclic substituents can be used as substrates, and the reaction proceeds under mild reaction conditions at ambient temperature to provide expedient access to enantioenriched alkylboronic esters in good regioselectivity and with excellent enantiocontrol. Critical to the success of the protocol was the development and application of a novel, sterically hindered N‐heterocyclic carbene, (R,R,R,R)‐ANIPE, as the ligand for copper.
By design: A highly enantioselective copper‐catalyzed Markovnikov protoboration of α‐olefins is described. This mild and general process effectively converts simple and abundant feedstock α‐olefins into a diverse array of chiral alkylboronic esters with excellent enantiocontrol. Key to the success of the protocol was the use of a newly developed, sterically hindered N‐heterocyclic carbene, (R,R,R,R)‐ANIPE, as the ligand.
The synthesis of 3,3‐difluoro‐2‐oxindoles through a robust and efficient palladium‐catalyzed CH difluoroalkylation is described. This process generates a broad range of difluorooxindoles from ...readily prepared starting materials. The use of BrettPhos as the ligand was crucial for high efficiency. Preliminary mechanistic studies suggest that oxidative addition is the rate‐determining step for this process.
Scoped out: An efficient synthesis of the title compounds by a palladium‐catalyzed CH difluoroalkylation is described. This method features a broad substrate scope, operational simplicity, and utilizes readily available starting materials. BrettPhos was found to facilitate this transformation with unique efficiency. CPME=cyclopentyl methyl ether, dba=dibenzylidene acetone.
We propose an extension of the symmetric teleparallel gravity, in which the gravitational action
L
is given by an arbitrary function
f
of the non-metricity
Q
and of the trace of the ...matter-energy-momentum tensor
T
, so that
L
=
f
(
Q
,
T
)
. The field equations of the theory are obtained by varying the gravitational action with respect to both metric and connection. The covariant divergence of the field equations is obtained, with the geometry–matter coupling leading to the nonconservation of the energy-momentum tensor. We investigate the cosmological implications of the theory, and we obtain the cosmological evolution equations for a flat, homogeneous and isotropic geometry, which generalize the Friedmann equations of general relativity. We consider several cosmological models by imposing some simple functional forms of the function
f
(
Q
,
T
), corresponding to additive expressions of
f
(
Q
,
T
) of the form
f
(
Q
,
T
)
=
α
Q
+
β
T
,
f
(
Q
,
T
)
=
α
Q
n
+
1
+
β
T
, and
f
(
Q
,
T
)
=
-
α
Q
-
β
T
2
. The Hubble function, the deceleration parameter, and the matter-energy density are obtained as a function of the redshift by using analytical and numerical techniques. For all considered cases the Universe experiences an accelerating expansion, ending with a de Sitter type evolution. The theoretical predictions are also compared with the results of the standard
Λ
CDM model.
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