Browsing by Author "Sachidanandan, Krishnakumar"

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    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 Science
    The 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.
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    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 Science
    Presented 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.
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    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 Science
    A 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.
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    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 Science
    Polyfluoroarene 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.