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The synthesis of α-aminosilanes by a highly enantio- and regioselective copper-catalyzed hydroamination of vinylsilanes is reported. The system employs Cu-DTBM-SEGPHOS as the catalyst, diethoxymethylsilane as the stoichiometric reductant, and O-benzoylhydroxylamines as the electrophilic nitrogen source. This hydroamination reaction is compatible with differentially substituted vinylsilanes, thus providing access to amino acid mimics and other valuable chiral organosilicon compounds. [ABSTRACT FROM AUTHOR]

Direct (utilize easily available and abundant precursors) and selective (both chemo- and regio-) aliphatic C–H functionalization is an attractive mean with which to streamline chemical synthesis. With many possible sites of reaction, traditional methods often need an adjacent polar directing group nearby to achieve high regio- and chemoselectivity and are often restricted to a single site of functionalization. Here we report a remote aliphatic C–H thiolation process with predictable and switchable regioselectivity through NiH-catalysed migratory hydrothiolation of two feedstock chemicals (alkenes/alkynes and thiols). This mild reaction avoids the preparation of electrophilic thiolation reagents and is highly selective to thiols over other nucleophilic groups, such as alcohols, acids, amines, and amides. Mechanistic studies show that the reaction occurs through the formation of an RS-Bpin intermediate, and THF as the solvent plays an important role in the regeneration of NiH species. Construction of C–S bonds via C–H functionalization is an attractive route to organosulfur compounds. Here, the authors show the synergistic combination of NiH-catalysed alkene isomerization and subsequent thiolation to afford remote hydrothiolation products from alkenes (or alkynes) and thiols under mild conditions. [ABSTRACT FROM AUTHOR]

Complementary to the design of a single structurally complex chiral ligand to promote each step in transition‐metal catalysis, multiligand relay catalysis through dynamic ligand exchange with each step in the catalytic cycle promoted by its best ligand provides an attractive approach to enhance the whole reaction reactivity and selectivity. Herein, a regio‐ and enantioselective NiH‐catalyzed migratory hydroarylation process with a simple combination of a chain‐walking ligand and an asymmetric arylation ligand, producing high‐value chiral α‐(hetero)aryl‐substituted amines and their derivatives under mild conditions, is reported. The potential synthetic applications of this transformation are demonstrated by the concise synthesis of (S)‐nicotine and a CDK8 inhibitor. [ABSTRACT FROM AUTHOR]

Abstract There are code biases on the pseudo-range observations of the Beidou Navigation Satellite System (BDS) that range in size from several decimeters to larger than one meter. These biases can be divided into two categories, which are the code biases in the pseudo-range observations of Inclined Geo-Synchronous Orbit (IGSO) satellites and Medium Earth Orbit (MEO) satellites and the code biases in the pseudo-range observations of Geosynchronous Earth Orbit (GEO) satellites. In view of the code bias of the IGSO/MEO satellites, the code bias correction model is established using the weighted least square curve fitting method. After the correction, the code biases of the IGSO and MEO satellites are clearly mitigated. A methodology of correcting GEO code bias is proposed based on the empirical mode decomposition (EMD)-wavelet transform (WT) coupled model. The accuracies of the GEO multipath combination of the B1, B2 and B3 frequencies are improved by 39.9%, 17.9%, and 29.4%, respectively. Based on the corrections above, the ten days observations of three Multi-GNSS Experiment (MGEX) stations are processed. The results indicate that the convergence time of the precise point positioning (PPP) can be improved remarkably by applying a code bias. The mean convergence time can be improved by 14.67% after the IGSO/MEO code bias correction. By applying the GEO code bias, the mean convergence time can be further improved by 17.42%. [ABSTRACT FROM AUTHOR]

Catalytic methods which control multiple stereogenic centers simultaneously are highly desirable in modern organic synthesis and chemical manufacturing. Herein, we report a regio‐, enantio‐, and diastereoselective NiH‐catalyzed hydroalkylation process which proceeds with simultaneous control of vicinal stereocenters originating from two readily accessible partners, prochiral internal alkenes (enamides or enecarbamates) and racemic alkyl electrophiles (α‐bromoamides or Katritzky salts). This reaction produces high‐value β‐aminoamides and their derivatives under mild conditions and with precise selectivity. Preliminary studies of the mechanism indicate that the reaction involves an enantioselective syn‐hydronickelation to generate an enantiomerically enriched alkylnickel(II) species. Subsequent enantioconvergent alkylation with a racemic alkyl electrophile generates the desired product as a single stereoisomer. [ABSTRACT FROM AUTHOR]

Enantioenriched multi‐substituted cycloalkanes constitute an essential class of compounds in pharmaceuticals, natural products and agrochemicals. Here we report an NiH‐catalyzed asymmetric migratory hydroalkylation process for the efficient and selective construction of such compounds. Through a dynamic kinetic asymmetric transformation (DYKAT), easily accessible racemic and isomeric mixtures of cycloalkenes could be directly utilized as starting materials, convergently producing thermo‐dynamically disfavored chiral 1,2‐cis disubstituted cycloalkanes bearing vicinal stereocenters with high levels of regio‐, diastereo‐ and enantioselectivity. In addition, prochiral cyclic alkenes can be also employed, and deliver chiral 1,2‐cis disubstituted cycloalkanes through desymmetrization process. [ABSTRACT FROM AUTHOR]

An attractive approach to selective functionalization of remote C−H bonds is a metal/hydride shift/cross‐coupling reaction sequence. Complimentary to the heavily exploited 1,2‐nickel/hydride shift along an sp3 chain, a chain‐walking process, the 1,4‐nickel/hydride shift along an sp2 chain is more complex. Here we report an unprecedented aryl‐to‐vinyl 1,4‐nickel/hydride shift reaction, in which the migratory alkenylnickel species generated in situ is selectively trapped by one of various coupling partners, such as isocyanates, alkyl bromides, aryl chlorides or alkynyl bromides, allowing regio‐ and stereoselective access to trisubstituted alkenes. In contrast to the well‐reported ipso‐aryl coupling reactions, this strategy provides remote alkenyl C−H functionalized products with good yield and with excellent chemo‐, regio‐ and E/Z‐selectivity. [ABSTRACT FROM AUTHOR]

An enantioselective nickel-catalyzed 1,2-alkynylboration of various vinylarenes with alkynylbromides and (Bpin) 2 is reported. This modular process provides an efficient access to structurally diverse enantioenriched chiral homopropargylboronates in a highly regio- and enantioselective manner. [Display omitted] An enantioselective nickel-catalyzed 1,2-alkynylboration of various vinylarenes with alkynylbromides and (Bpin) 2 is reported. This modular process provides an efficient access to structurally diverse enantioenriched chiral homopropargylboronates in a highly regio- and enantioselective manner. [ABSTRACT FROM AUTHOR]

Most of research on the identification of offensive speech on social media platforms exist in English and other rich languages. A series of recently proposed methods for detecting low-resource offensive languages require labeled data. In this work, we propose an unsupervised model that can detect offensive speech for low-resource languages. Our method does not depend on any labeled data of low-resource languages. In detail, we propose an agreement regularized training that combines adversarial learning and transfer learning. Augmenting low-resource training data with sample regeneration methods to maintain the performance of the trained offensive speech identification model from rich-resource to low-resource languages. Extensive experiments on four low-resource languages demonstrate that our model either is on par or outperforms the supervised methods, without employing any annotated data on real-world offensive speech detection tasks for low-resource languages. [Display omitted] [ABSTRACT FROM AUTHOR]

Primary amines serve as key synthetic precursors to most other N -containing compounds, which are important in organic and medicinal chemistry. Herein, we present a NiH-catalyzed mild ipso- and remote hydroamination technique that utilizes organic azides as deprotectable primary amine sources. This strategy offers a highly flexible platform for the efficient construction of α-chiral branched primary amines, as well as linear primary amines.

Selective functionalization of ubiquitous C-H bonds based on 1, n -metal migration provides an attractive and sustainable route to access complex molecules from readily available precursors. Herein, we report a Co-catalyzed asymmetric reductive migratory Nozaki-Hiyama-Kishi (NHK) coupling between two readily available electrophiles, aryl (pseudo)halides and aldehydes, via an unprecedented through-space aryl-to-alkenyl 1,4-cobalt/hydride shift. The judicious choice of ligands is crucial for selectivity, leading to either ipso- or migratory NHK products with exquisite control of regio-, E / Z -, and enantioselectivity. Enabled by a ligand relay catalytic strategy, this platform has been further extended to aryl-to-aryl asymmetric migratory NHK coupling. These high-value NHK adducts, including α-chiral allylic alcohols and benzyl alcohols, are readily convertible to a variety of useful synthons.

Monofluoroalkenes serve as nonhydrolyzable mimetics of amides and are frequently encountered in drug candidates. Herein we report a regio-, enantio-, and stereoselective NiH-catalyzed ipso- and migratory defluorinative olefin cross-coupling employing readily available olefins and gem-difluoroalkenes under mild conditions. This approach enables the efficient synthesis of a broad array of structurally diverse monofluoroalkenes bearing a tertiary allylic stereogenic center. Mechanistically, the challenging migratory defluorinative olefin cross-coupling process is successfully realized through a ligand relay catalytic strategy, enabling the formal C(sp 3 )-H/C(sp 2 )-F activation with high levels of regio-, stereo-, and enantiocontrol., (© 2024. The Author(s).)

ConspectusMigratory cross-coupling via metal migration is a process of significant academic and industrial interest. It provides an attractive alternative for the selective installation of a functional group at remote C-H positions from simple precursors, thus enabling the direct synthesis of challenging structures not accessible with traditional cross-coupling. In particular, with the merger of 1, n -Ni/H shift and cross-coupling of nickel, the Ni-catalyzed migratory functionalization of simple precursors has undergone particularly intense development and emerged as a valuable field of research in the past few years. This Account will outline the recent progress made in this arena in terms of migration-functionalization modes, diverse functionalizations, and strategies for regio- and stereocontrol. Mechanistic studies and synthetic applications are also discussed.In detail, we systematically categorize our work into two parts based on the migration modes. In the first part, a platform is created for Ni-catalyzed migratory sp 3 C-H functionalization of alkenes or alkyl halides via iterative 1,2-Ni/H shift-selective cross-coupling. The key reactive Ni(II)H species for chain-walking could be generated in situ either in a polarity-reversed fashion relying on stoichiometric reductants (X-Ni(II)-H) or in a redox-neutral fashion with the participation of nucleophilic coupling partners (FG-Ni(II)-H). One significant advantage associated with the polarity-reversed NiH system is the use of relatively stable, abundant, and safe olefin surrogates or alkyl halides instead of the sensitive organometallics required in traditional cross-coupling reactions. Another advantage is that diverse functionalizations, including carbonation and more challenging amination and thiolation could be smoothly achieved with suitable electrophiles or their precursors. Finally, to address the challenging multifaceted selectivity and reactivity issues in asymmetric migratory cross-coupling reactions, we have developed a feasible ligand relay catalytic strategy. In this dynamic ligand exchange process, one ligand promotes rapid migration while the other promotes highly regio- and stereoselective coupling. This innovative strategy overcomes the formidable challenge stemming from the difficulty of designing a single ligand to efficiently promote both steps of chain-walking and asymmetric coupling. In the second part, a new platform for Ni-catalyzed migratory sp 2 C-H functionalization via 1,4-Ni/H shift-selective cross-coupling has been reported. Starting from readily available aryl or vinyl coupling partners, the in situ -generated aryl- or vinylnickel(II) species could undergo a rapid and reversible 1,4-Ni/H shift along an sp 2 backbone, and subsequent selective coupling with various coupling partners would allow regio- and stereoselective access to diverse 1,4-migratory functionalization products. The key to success was the discovery of an appropriate ligand to efficiently promote both migration and subsequent selective cross-coupling. A vinyl-to-aryl 1,4-Ni/H shift successfully enables the modular ipso / ortho difunctionalization of aryl coupling partners, while an aryl-to-vinyl 1,4-Ni/H shift enables regio- and stereoselective access to functionalized trisubstituted alkenes.We hope that this Account will inspire broad interest and future development of migratory cross-coupling reactions. We strongly believe that continued efforts in this fascinating field will overcome many of the remaining challenges, including cutting-edge ligand/catalyst design to enhance reactivity and selectivity, conceptually new migration modes for additional transformations, and in-depth mechanistic studies for rational reaction design.

Chiral α-aminoboronic acids and their derivatives are generally useful as bioactive compounds and some have been approved as therapeutic agents. Here we report a NiH-catalysed asymmetric hydroamidation process that with a simple amino alcohol ligand can easily produce a wide range of highly enantioenriched α-aminoboronates from alkenyl boronates and dioxazolones under mild conditions. The reaction is proposed to proceed by an enantioselective hydrometallation followed by an inner-sphere nitrenoid transfer and C-N bond forming sequence. The synthetic utility of this transformation was demonstrated by the efficient synthesis of a current pharmaceutical agent, Vaborbactam., (© 2022. The Author(s).)

The design of a single complicated chiral ligand to well-promote each step of an asymmetric cascade reaction is sometimes a formidable challenge in transition metal catalysis. In this work, a highly regio- and enantioselective Ni-catalysed migratory hydroarylation relay process has been achieved with the combination of two simple ligands, one which accomplishes chain-walking and the other causing asymmetric arylation. This formal asymmetric C(sp 3 )-H arylation provides direct access to a wide range of structurally diverse chiral 1,1-diarylalkanes, a structural unit found in a number of bioactive molecules. The value of this strategy was further demonstrated by the Ni-catalysed migratory asymmetric 1,3-arylboration., (© 2022. The Author(s).)

α-Chiral alkyne is a key structural element of many bioactive compounds, chemical probes, and functional materials, and is a valuable synthon in organic synthesis. Here we report a NiH-catalysed reductive migratory hydroalkynylation of olefins with bromoalkynes that delivers the corresponding benzylic alkynylation products in high yields with excellent regioselectivities. Catalytic enantioselective hydroalkynylation of styrenes has also been realized using a simple chiral PyrOx ligand. The obtained enantioenriched benzylic alkynes are versatile synthetic intermediates and can be readily transformed into synthetically useful chiral synthons.

Enantiomerically pure chiral amines and related amide derivatives are privilege motifs in many pharmacologically active molecules. In comparison to the well-established hydroamination, the transition metal-catalysed asymmetric hydrofunctionalization of enamines provides a complementary approach for their construction. Here we report a NiH-catalysed enantio- and regioselective reductive hydroarylation of N-acyl enamines, allowing for the practical access to a broad range of structurally diverse, enantioenriched benzylamines under mild, operationally simple reaction conditions.

Starting from diverse alkene-tethered aryl iodides and O-benzoyl-hydroxylamines, the enantioselective reductive cross-electrophilic 1,2-carboamination of unactivated alkenes was achieved using a chiral pyrox/nickel complex as the catalyst. This mild, modular, and practical protocol provides rapid access to a variety of β-chiral amines with an enantioenriched aryl-substituted quaternary carbon center in good yields and with excellent enantioselectivities. This process reveals a complementary regioselectivity when compared to Pd and Cu catalysis., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Despite significant recent progress in copper-catalyzed enantioselective hydroamination chemistry, the synthesis of chiral N-arylamines, which are frequently found in natural products and pharmaceuticals, has not been realized. Initial experiments with N-arylhydroxylamine ester electrophiles were unsuccessful and, instead, their reduction in the presence of copper hydride (CuH) catalysts was observed. Herein, we report key modifications to our previously reported hydroamination methods that lead to broadly applicable conditions for the enantioselective net addition of secondary anilines across the double bond of styrenes, 1,1-disubstituted olefins, and terminal alkenes. NMR studies suggest that suppression of the undesired reduction pathway is the basis for the dramatic improvements in yield under the reported method., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The terminal-selective, remote C(sp 3 )-H alkylation of alkenes was achieved by a relay process combining NiH-catalyzed hydrometalation, chain walking, and alkylation. This method enables the construction of unfunctionalized C(sp 3 )-C(sp 3 ) bonds under mild conditions from two simple feedstock chemicals, namely olefins and alkyl halides. The practical value of this transformation is further demonstrated by the large-scale and regioconvergent alkylation of isomeric mixtures of olefins at low catalyst loadings., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)