- Browse by Author
Browsing by Author "Niu, Ben"
Now showing 1 - 8 of 8
Results Per Page
Sort Options
Item An Overview of α-Aminoalkyl Radical Mediated Halogen-Atom Transfer(Wiley, 2023-11-08) Sachidanandan, Krishnakumar; Niu, Ben; Laulhé, Sébastien; Chemistry and Chemical Biology, School of ScienceThe merging of photocatalysis with halogen-atom transfer (XAT) processes has proven to be a versatile tool for the generation of carbon-centered radicals in organic synthesis. XAT processes are unique in that they generate radicals without requiring the use of strong reductants necessary for the traditional single electron transfer (SET) activation of halides. Pathways to achieve XAT in synthetic applications can be categorized into three major sections: i) heteroatom-based activators, ii) metal-based activators, and iii) carbon-based activators among which α-aminoalkyl radicals have taken the center stage. Access to these α-aminoalkyl radicals as XAT reagents has gained significant attention in the past few years due to the robustness of the reactions, the simplicity of the reagents required, and the broadness of their applications. Generation of these α-aminoalkyl radicals is simply achieved through the single electron oxidation of tertiary amines, which after deprotonation at the α-position generates the α-aminoalkyl radicals. Due to the wide scope of tertiary amines available and the tunable nucleophilicity of α-aminoalkyl radical formed, this strategy has become an attractive alternative to heteroatom/metal-based radicals for XAT. In this minireview, we focus our attention on recent (2020–2023) developments and uses of this robust technology to mediate XAT processes.Item Benzisothiazol‐3‐ones through a Metal‐Free Intramolecular N–S Bond Formation(Wiley, 2018-11) Yang, Ke; Zhang, Hao; Niu, Ben; Tang, Tiandi; Ge, Haibo; Chemistry and Chemical Biology, School of ScienceThe highly efficient synthesis of benzoisothiazol‐3‐ones from thiobenzamides has been described with good functional group compatibility and excellent yields. This work represents the first example of selectfluor‐promoted N–S bond formation processes. This method provides a facile approach to access various important bioactive benzoisothiazol‐3‐ones.Item Generation of Alkyl Radicals Via C-H Functionalization and Halogen Atom Transfer Processes(2022-12) Niu, Ben; Laulhé, Sébastien; Long, Eric; Minto, Robert E.; Pu, JingzhiAlkyl radicals are powerful intermediates for the generation of carbon-carbon bonds, which play an indispensable role in the synthesis of natural products, pharmaceuticals, and pesticides. Traditionally, there are two main methods for the generation of alkyl radicals. The first is C-H bond functionalization via hydrogen-atom-transfer (HAT). HAT processes have been used as an effective approach for selectively activating C-H bonds via radical pathways. The other strategy to explore the generation of alkyl radicals is C-X bond functionalization via halogen-atom-transfer (XAT). Alkyl halides are one of the largest classes of building blocks in synthesis and they can be obtained from the corresponding alcohols. The most straightforward and effective way to form such alkyl radicals is the direct homolytic cleavage of C-X bonds. In past decades, photoredox catalysis has emerged as a powerful and greener tool for the synthesis of radicals under mild reaction conditions, which has brought tremendous attention. Although remarkable success has been made in this field, some methods still require costly transition metal catalysts or toxic reagents. Herein, we display a series of visible light-induced approaches under transition-metal free conditions or using earth-abundant metals. These novel photo-induced transformations and corresponding mechanistic work will be discussed in the following order: We will first present our work on metal-free visible-light-promoted C(sp3)-H functionalization of aliphatic cyclic ethers using trace O2. This reaction uses a trace amount of aerobic oxygen as the sole green oxidant under blue light at room temperature to achieve the synthesis of sulfone and phosphate derivatives in good to excellent yields using cyclic ethers and vinyl sulfones. Then, we report on a photo-induced C(sp3)-H chalcogenation of amide derivatives and ethers via a ligand-to-metal charge-transfer. This reaction converts secondary and tertiary amides, sulfonamides, and carbamates into the corresponding amido-N,S-acetal derivatives in good yields, using an earth abundant metal catalyst under mild conditions. Finally, we present a photoredox polyfluoroarylation of alkyl halides via halogen atom transfer. This method converts primary, secondary, and tertiary unactivated abundant alkyl halides into the corresponding polyfluoroaryl compounds in good yields and has good functional group compatibility.Item Metal-free visible-light-promoted C(sp3)-H functionalization of aliphatic cyclic ethers using trace O2(Royal Society of Chemistry, 2021) Niu, Ben; Blackburn, Bryan G.; Sachidanandan, Krishnakumar; Cooke, Maria Victoria; Laulhé, Sébastien; Chemistry and Chemical Biology, School of SciencePresented is a light-promoted C-C bond forming reaction yielding sulfone and phosphate derivatives at room temperature in the absence of metals or photoredox catalyst. This transformation proceeds in neat conditions through an auto-oxidation mechanism which is maintained through the leaching of trace amounts of O2 as sole green oxidant.Item Photoinduced C(sp3)-H Chalcogenation of Amide Derivatives and Ethers via Ligand-to-Metal Charge-Transfer(American Chemical Society, 2022) Niu, Ben; Sachidanandan, Krishnakumar; Cooke, Maria Victoria; Casey, Taylor E.; Laulhé, Sébastien; Chemistry and Chemical Biology, School of ScienceA photoinduced, iron(III) chloride-catalyzed C-H activation of N-methyl amides and ethers leads to the formation of C-S and C-Se bonds via a ligand-to-metal charge transfer (LMCT) process. This methodology converts secondary and tertiary amides, sulfonamides, and carbamates into the corresponding amido-N,S-acetal derivatives in good yields. Mechanistic work revealed that this transformation proceeds through a hydrogen atom transfer (HAT) involving chlorine radical intermediates.Item Photoredox Polyfluoroarylation of Alkyl Halides via Halogen Atom Transfer(American Chemical Society, 2022) Niu, Ben; Sachidanandan, Krishnakumar; Blackburn, Bryan G.; Cooke, Maria Victoria; Laulhé, Sébastien; Chemistry and Chemical Biology, School of SciencePolyfluoroarene moieties are of interest in medicinal chemistry, agrochemicals, and material sciences. Herein, we present the first polyfluoroarylation of unactivated alkyl halides via a halogen atom transfer process. This method converts primary, secondary, and tertiary alkyl halides into the respective polyfluoroaryl compounds in good yields in the presence of amide, carbamate, ester, aromatic, and sulfonamide moieties, including derivatives of complex bioactive molecules. Mechanistic work revealed that this transformation proceeds through an alkyl radical generated after the halogen atom transfer.Item Silver-Promoted Site-Selective Intramolecular Cyclization of 2-Methylthiobenzamide Through α-C(sp3)–H Functionalization(ACS, 2019-11) Yang, Ke; Niu, Ben; Ma, Zhiyan; Wang, Hui; Lawrence, Brianna; Ge, Haibo; Chemistry and Chemical Biology, School of ScienceSilver-mediated intramolecular α-C(sp3)–H bond functionalization of the methylthio group has been established in the presence of Selectfluor as an additive. This novel strategy provides efficient access to various diverse sulfur-based heterocycles with good yields and functional group compatibility. It is noteworthy that the completely novel benzooxathiin-4-imine skeletons were reported for the first time in this study.Item Transient ligand‐enabled transition metal‐catalysed C‐H functionalisation(Wiley, 2019) Niu, Ben; Yang, Ke; Lawrence, Brianna; Ge, Haibo; Chemistry and Chemical Biology, School of ScienceTransition metal‐catalysed C‐H bond functionalisation is one of the most efficient and powerful strategies in synthetic organic chemistry to derivatize otherwise inert sites of organic molecules for the construction of C‐C and C‐heteroatom bonds. However, additional steps are often required in order to install the directing groups to realize the positional functionalisation of the substrates. These tedious steps run counter to the step‐economical nature of the C‐H activation. In contrast, direct functionalisation of the substrate, utilizing the transient ligands, avoids the unnecessary steps for the prefunctionalisation of the substrates. In this mini review, we will provide a short journey for the major progress made in this field for the C‐H functionalisation on sp2 and sp3 carbon centres with different transient working modes, including the covalent, hydrogen, and ionic bonds.