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By merging nickel catalysis and photochemistry, we developed a deoxygenative alkylboration of aldehydes via a deoxygenative difunctionalization of carbonyls strategy. This three-component reaction between alkyl halides, B2Pin2, and aldehydes represents one of the most efficient methods to furnish the versatile secondary α,α-dialkyl boronates. A series of deoxygenative difunctionalization skeletons can be gained from the products based on the carbon–boron bond transformation. In addition, deoxygenative arylboration of aldehydes was achieved.

A novel gold-catalyzed cycloisomerization/[2 + 1]cycloaddition/rearrangement of enyne-amides and sulfur ylides is reported. This strategy enables rapid and efficient construction of a series of α-pyrone derivatives.

A highly efficient [4 + 1] annulation of sulfur ylide salts and o-sulfonamido aldimines for construction of valuable 2,3-disubstituted indolines is reported. It is worth noting that indoles could also be synthesized by this cascade reaction.

We disclose herein an atroposelective synthesis of novel bridged biaryls containing medium-sized rings via N-heterocyclic carbene organocatalysis. The reaction starts with addition of the carbene catalyst to the aminophenol-derived aldimine substrate. Subsequent oxidation and intramolecular desymmetrization lead to the formation of 1,3-oxazepine-containing bridged biaryls in good yields and excellent enantioselectivities. These novel bridged biaryl products can be readily transformed into chiral phosphite ligands. Preliminary density function theory calculations suggest that the origin of enantioselectivity arises from the more favorable frontier molecular orbital interactions in the transition state leading to the major product. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) Submitted/Accepted version We acknowledge financial supports of the starting-up funding from Hunan Normal University, the National Natural Science Foundation of China (21901233, 22201071), Singapore National Research Foundation under its NRF Investigatorship (NRF-NRFI2016-06) and Competitive Research Program (NRF-CRP22-2019-0002); the Ministry of Education, Singapore, under its MOE AcRF Tier1 Award (RG108/16, RG5/19, RG1/18), MOE AcRF Tier 2 (MOE2019-T2-2-117), MOE AcRF Tier 3 Award (MOE2018-T3-103); the Agency for Science, Technology and Research (A*STAR) under its A*STAR AMEIRG Award (A1783c0008, A1783c0010); GSK-EDB Trust Fund; Nanyang Research Award Grant, Nanyang Technological University; X.Z. acknowledges the support from IHPC, A*STAR, and thanks the Deputy Chief Executive Research Office (DCERO), A*STAR, for a Career Development Fund (CDF Project Number C210812008) for this work.

Photoredox-catalyzed addition of the difluororadical to unactivated alkenes has been found to trigger neophyl-like aryl and heteroaryl migrations which allowed the construction of a diverse series of difluoromethyl ketones.

Addition of the difluoromethyl radical, under photo-redox conditions, to a series of conjugated arylsulfonylated amides resulted in formation of two different products, which are selectively formed by altering reaction conditions.

A novel catalyst-controlled cycloisomerization/[4 + 3]cycloaddition sequence of readily available acyclic enyne-amides and crotonate-derived sulfur ylides is developed.

C-F insertion of carbon-atom units is underdeveloped although it poses significant potential applications in both drug discovery and development. Herein, we report a photocatalytic protocol for late-stage modification of trifluoromethyl aromatic drugs involving formal insertion of abundant alkene feedstocks into a benzylic C-F bond selectively. This redox-neutral transformation features mild conditions and extraordinary functional group tolerance. Preliminary studies are consistent with this transformation involving a radical-polar crossover pathway. Additionally, it offers an alternative strategy for difunctionalization of alkenes via quenching of the carbocation intermediate with nucleophiles other than external fluoride.

Reported herein is a novel [5 + 1] cycloaddition-aromatization of benzotriazoles and sulfur ylides to efficiently construct 1,2,4-benzotriazine derivates with good yield. This new protocol does not employ any transition metal reagent and enables the cycloaddition by cleavage of the N-N single bond. The use of inexpensive and readily available starting materials, a broad substrate scope, mild reaction conditions, metal-free, and versatile functionalization of the 1,2,4-benzotriazines make this strategy more attractive.

This report describes the site-selective α-functionalization of sulfonylamide derivatives through the in-situ generation of imine intermediates. The N-F sulfonylamides, which could facilitate the elimination to generate imines, are coupled with TBACN to efficiently and mildly afford α-amino cyanides. Comparing with Strecker reaction, this transformation offers a complementary strategy to efficiently construct α-amino cyanides from direct α C-H functionalization of sulfonylamindes. The reaction is also characterized by broad substrate scope and flash chromatography column free workup. More importantly, the new two-electron pathway to generate imines through manipulation of the leaving group allows us to achieve excellent α site-selectivity.

A new mode of carbene-catalyzed heteroatom activation and asymmetric reactions is disclosed. The reaction starts with addition of a carbene catalyst to a (benz)imidazole-derived aldimine substrate. Subsequent oxidation and proton transfer lead to the formation of a catalyst-bound triaza-diene as the key intermediate, in which the nitrogen atom at a site remote to the catalyst-substrate bond is activated. This unusual triaza-diene intermediate then undergoes highly enantioselective reactions with activated ketones through a concerted asynchronous pathway, as supported by mechanistic studies and preliminary density function theory calculation. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) Accepted version We acknowledge financial supports from Singapore National Research Foundation under its NRF Investigatorship (NRF-NRFI2016-06) and Competitive Research Program (NRF-CRP22-2019-0002); the Ministry of Education, Singapore, under its MOE AcRF Tier 1 Award (RG108/16, RG5/19, RG1/18), MOE AcRF Tier 2 (MOE2019-T2-2-117), MOE AcRF Tier 3 Award (MOE2018-T3-1-003); the Agency for Science, Technology and Research (A*STAR) under its A*STAR AME IRG Award (A1783c0008, A1783c0010); GSK-EDB Trust Fund; Nanyang Research Award Grant, Nanyang Technological University; the National Natural Science Foundation of China (21772029, 21801051, 21807019, 21961006, 22071036, 22061007, 82360589, 81360589), Frontiers Science Center for Asymmetric Synthesis and Medicinal Molecules, Department of Education, Guizhou Province [Qianjiaohe KY number (2020)004]; The 10 Talent Plan (Shicengci) of Guizhou Province ([2016]5649); the Science and Technology Department of Guizhou Province ([2018]2802, [2019]1020); the Program of Introducing Talents of Discipline to Universities of China (111 Program, D20023) at Guizhou University; the Guizhou Province First-Class Disciplines Project [(Yiliu Xueke Jianshe Xiangmu)-GNYL(2017)008], NSFC Grant (81360589), Guizhou University of Traditional Chinese Medicine (China); and Guizhou University. X.Z. thanks the Institute of High Performance Computing (IHPC), A*STAR for financial support and acknowledges the use of super computers in the A*STAR Computational Resource Centre (ACRC) and the National Supercomputing Centre (NSCC), Singapore (https://www.nscc.sg), for computations performed in this work.

A variety of furo[2,3

Here we report a mild and general method for the trifluoromethylthiolation of aldehydes using

A carbene-catalyzed enantioselective cascade reaction of substituted methylenemalononitriles and α-bromoenals is disclosed. Key steps of this cascade process include a formal [4 + 2] cycloaddition, aldol reaction, and intramolecular lactonization. Our reaction offers streamlined and highly stereoselective access to complex tetrahydrocarbazole derivatives, with simultaneous formation of four chemical bonds and four chiral centers. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version We thank Dr. Yongxin Li (NTU) for assistance with X-ray structure analysis. We acknowledge financial support by the Singapore National Research Foundation (NRF-NRFI2016- 06), the Ministry of Education of Singapore (RG 1/18; RG 5/ 19; MOE2018-T3-1-003), an A*STAR Individual Research Grant (A1783c0008; A1783c0010), GSK-EDB Trust Fund, a Nanyang Research Award Grant, and Nanyang Technological University; the Guizhou Province First-Class Disciplines Project (Yiliu Xueke Jianshe Xiangmu)-GNYL(2017)008, Guizhou University of Traditional Chinese Medicine (China), QMYY [2017]101 (China); the National Natural Science Foundation of China (Nos. 21772029, 21901233), the National Key Technologies R&D Program (No. 2014BAD23B01), the “Thousand Talent Plan”, the 10 Talent Plan (Shicengci) of Guizhou Province [2016]5649, and Guizhou University, Department of Science and Technology of Guizhou Province [2019]1020, Undergraduate Innovation and Pioneer Training Program, Guizhou University of Traditional Chinese Medicine 2018(31), Program of Introduc- ing Talents of Discipline to Universities of China (111 Program, D20023).

A novel one-pot approach for the synthesis of multi-substituted 2-imidazolylimidazoles, 2-pyrazolylimidazoles and 2-indazolylimidazoles was developed through a domino addition/A3 coupling/cyclization process under copper catalysis. A variety of aminoethyl- or hydroxylethyl-tethered 2-azolylimidazole derivatives were conveniently and efficiently assembled in one pot using N-propargylcarbodiimides, azoles, paraformaldehyde and secondary amines as starting materials. The products containing an o-iodoaryl group could be further converted to imidazo[1,2-c]imidazo[1,2-a]quinazoline derivatives through a copper-catalyzed intramolecular C-H arylation.

Herein, we disclosed a highly efficient strategy of enantioselective synthesis of 2,3-furan-fused carbocycles bearing three-contiguous stereocenters. This transformation is catalyzed by dual catalysis of PtCl4/chiral amines via tandem dehydrogenative annulation/Diels–Alder reaction of 2-(1-alkynyl)-2-alken-1-ones and enals. The in situ generation of the furan-based ortho-quinodimethane intermediates and the iminium activation of enals are crucial to this transformation.

This report describes the site-selective α-functionalization of sulfonylamide derivatives through the in-situ generation of imine intermediates. The N-F sulfonylamides, which could facilitate the elimination to generate imines, are coupled with TBACN to efficiently and mildly afford α-amino cyanides. Comparing with Strecker reaction, this transformation offers a complementary strategy to efficiently construct α-amino cyanides from direct α C-H functionalization of sulfonylamindes. The reaction is also characterized by broad substrate scope and flash chromatography column free workup. More importantly, the new two-electron pathway to generate imines through manipulation of the leaving group allows us to achieve excellent α site-selectivity.

A catalyst- and metal-free electrochemical hydrodehalogenation of aryl halides is disclosed. Our reaction by a flexible protocol is operated in an undivided cell equipped with an inexpensive graphite rod anode and cathode. Trialkylamines nBu3 N/Et3 N behave as effective reductants and hydrogen atom donors for this electrochemical reductive reaction. Various aryl and heteroaryl bromides worked effectively. The typically less reactive aryl chlorides and fluorides can also be smoothly converted. The utility of our method is demonstrated by detoxification of harmful pesticides and hydrodebromination of a dibrominated biphenyl (analogues of flame-retardants) in gram scale. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

The dominated approaches for asymmetric aldol reactions have primarily focused on the aldol carbon-carbon bond-forming events. Here we postulate and develop a new catalytic strategy that seeks to modulate the reaction thermodynamics and control the product enantioselectivities via post-aldol processes. Specifically, an NHC catalyst is used to activate a masked enolate substrate (vinyl carbonate) to promote the aldol reaction in a non-enantioselective manner. This reversible aldol event is subsequently followed by an enantioselective acylative kinetic resolution that is mediated by the same (chiral) NHC catalyst without introducing any additional substance. This post-aldol process takes care of the enantioselectivity issues and drives the otherwise reversible aldol reaction toward a complete conversion. The acylated aldol products bearing quaternary/tetrasubstituted carbon stereogenic centers are formed in good yields and high optical purities. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version

A novel one-pot approach for the synthesis of multi-substituted 2-imidazolylimidazoles, 2-pyrazolylimidazoles and 2-indazolylimidazoles was developed through a domino addition/A3 coupling/cyclization process under copper catalysis. A variety of aminoethyl- or hydroxylethyl-tethered 2-azolylimidazole derivatives were conveniently and efficiently assembled in one pot using N-propargylcarbodiimides, azoles, paraformaldehyde and secondary amines as starting materials. The products containing an o-iodoaryl group could be further converted to imidazo[1,2-c]imidazo[1,2-a]quinazoline derivatives through a copper-catalyzed intramolecular C-H arylation.

SmI2-mediated reductive cyclization of β-arylthio ketones to generate thiochroman derivatives is not a generally observed process and the reported examples are limited to geminal disubstitution in the substrates. The results of the current study show that the cyclization also occurs when other substitution patterns are present, affording a general approach to dihydrothiochroman-ols in good yields and high degrees of diastereoselectivity. Besides, the halogen substitution on β-aryl is tolerated in most cases here although reductive dehalogenation has been reported to predominate in the reductive cyclization process. Dihydrothiochroman-4-ols were readily oxidized to thiochroman-4-ols in almost quantitative yields.

An enantioselective functionalization of the indole NH group is developed. The reaction stereoselectivity is controlled by an N-heterocyclic carbene catalyst that adds to an aldehyde moiety at the C7-carbon of indole. The NH group participating in the carbene-catalyzed reaction is part of the heteroaromatic rings of the indole substrate. Our reactions afford multicyclic products bearing pyrroloquinazoline or oxazinoindole scaffolds widely present in bioactive molecules. Our study will encourage further exploration of carbene-catalyzed reactions of aromatic molecules and asymmetric transformation of heteroatoms in various functional molecules. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

A new catalytic approach for rapid asymmetric access to spirocycles is disclosed. The reaction involves a carbene- and thiourea-cocatalyzed desymmetrization process with the simultaneous installation of a spirocyclic core. The use of a thiourea cocatalyst is critical to turn on this reaction, as no product was formed in the absence of a thiourea. Our study constitutes the first success in the carbene-catalyzed enantioselective synthesis of all-carbon spirocycles. The reaction products can be readily transformed into sophisticated multicyclic molecules and chiral ligands. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

A carbene and sulfinate co-catalyzed intermolecular Rauhut-Currier reaction between enals and nitrovinyl indoles is disclosed. The carbene catalyst activates the enal and the sulfinate co-catalyst activates the nitrovinyl indole. Both activation processes are realized via the formation of covalent bonds between the catalysts and substrates to generate catalyst-bound intermediates. The dual catalytic reaction affords azepino[1,2-a]indole products with excellent stereoselectivity. Our study demonstrates the unique involvement of sulfinate as an effective nucleophilic catalyst in activating electron-deficient alkenes for asymmetric reactions. This dual catalytic approach should also encourage future explorations of both sulfinate and carbene catalysts for new reactions. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

An unprecedented strategy for in situ generation of indole-based ortho-quinodimethanes (oQDMs) from 2-methyl-3-alkylmethylindoles by either a metal-free DDQ- or BQ-mediated dehydrogenative process was developed. These oQDMs were trapped by electron-deficient dienophiles to provide a facile approach to synthetically valuable tetrahydrocarbazoles, carbazoles, and hetereoacenes. The salient features of this transformation include direct C(sp(3))-H bond functionalizations, readily available starting materials, metal-free conditions, high efficiency, operational simplicity, and ease of scale-up.

Diastereoselective synthesis of cis-1,2-disubstituted cyclopropanols and cyclopent-3-enols has been achieved from readily available β-benzotriazolyl ketones (β-Bt ketones) via a C–N(Bt) bond cleavage/cyclization process promoted by SmI2/HMPA.

3-Aryl-1,2,4-benzotriazines were conveniently prepared in moderate to good yields from 1,l-bis(benzotriazol-1-yl)methylarenes with allylsamarium bromide/hexamethylphosphramide (allylSmBr/HMPA). Preliminary results indicate that HMPA may enhance the reducing ability as well as prohibit the nucleophicility of allylSmBr, thus making allylSmBr/HMPA as a promising single-electron transfer (SET) reagent.

In recent years, remarkable progress has been made in dehydro or dehydrogenative Diels-Alder (D-A) reactions. This Minireview gives an overview of the major two strategies for dehydro(genative) Diels-Alder reactions, which differ in dehydrogenation and D-A cyclization sequence. Reactions in which D-A cycloaddition is followed by dehydrogenation are useful methods for the synthesis of various aromatic compounds, whereas advancements in dehydro genative procedures with oxidants or catalysts prior to D-A cycloaddition offer yet further new routes to functionalized cycloadducts. Recent leading findings are highlighted and the current state of the art, scope, and limitations of these processes are discussed in this Minireview.

Efficient regioselective conjugate additions of thiophenols and benzotriazole to 4-aryl-4-oxobut-2-enoates have been achieved under mild conditions. Thus a variety of 2-arylthio-4-oxo-4-arylbutanoates and 2- benzotriazolyl-4-oxo-4-arylbutanoates were conveniently synthesized in good to excellent yields.

A wide range of indole-based ortho-quinodimethanes is generated in situ by a DDQ- or benzoquinone-mediated dehydrogenation process.

Diastereoselective synthesis of cis-1,2-disubstituted cyclopropanols and cyclopent-3-enols has been achieved from readily available β-benzotriazolyl ketones (β-Bt ketones) via a C–N(Bt) bond cleavage/cyclization process promoted by SmI2/HMPA.

In recent years, remarkable progress has been made in dehydro or dehydrogenative Diels-Alder (D-A) reactions. This Minireview gives an overview of the major two strategies for dehydro(genative) Diels-Alder reactions, which differ in dehydrogenation and D-A cyclization sequence. Reactions in which D-A cycloaddition is followed by dehydrogenation are useful methods for the synthesis of various aromatic compounds, whereas advancements in dehydro genative procedures with oxidants or catalysts prior to D-A cycloaddition offer yet further new routes to functionalized cycloadducts. Recent leading findings are highlighted and the current state of the art, scope, and limitations of these processes are discussed in this Minireview.

Facile and efficient conjugate additions of carbon nucleophiles, such as ?-dicarbonyl compounds and nitroalkanes, to 4-aryl-4-oxobut-2-enoates have been achieved under simple base catalysis. A variety of multi-functional ?-keto esters could be conveniently obtained in good to excellent yields with complete regioselectivity.

Benzotriazole adducts methoxycarbonylamino-1-(1-benzotriazolyl)alkanes 1 were derived from the condensation of an aldehyde, benzotriazole, and methylcarbamate. The leaving tendency of methoxycarbonylamino group (MeOCONH) and benzotriazole group (Bt) was investigated by treatment of the adducts with active methylene compounds under either Lewis acid-catalyzed or basic conditions. In the presence of SmI3, MeOCONH take priority over Bt in the leaving process, whereas in the presence of MeONa, the Bt was substituted in preference. Thus, the tunable substitution of the two leaving groups could be used for different synthetic purposes. J. Heterocyclic Chem., 00, 00 (2011).

Intermediary o-quinodimethanes are trapped with alkenes and alkynes, respectively, to provide highly functionalized furan derivatives.

A strategy for in situ generation of furan-based ortho-quinodimethanes (o-QDMs) by the gold(I)-mediated dehydrogenative heterocyclization of 2-(1-alkynyl)-2-alken-1-ones in the presence of pyridine N-oxide under mild reaction conditions was developed. These in situ furan-based o-QDMs were trapped by electron-deficient olefins and alkynes, thus furnishing various 2,3-furan-fused carbocycles in good yields with high diastereo- and regioselectivities.

The authors state that HMPA enhances the reducing ability of samarium as well as it prohibits the nucleophilicity of allyl-SmBr generated in situ.