- Remarkably Efficient Iridium Catalysts for Directed C(sp2)-H and C(sp3)-H Borylation of Diverse Classes of Substrates
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Here we describe the discovery of a new class of C-H borylation catalysts and their use for regioselective C-H borylation of aromatic, heteroaromatic, and aliphatic systems. The new catalysts have Ir-C(thienyl) or Ir-C(furyl) anionic ligands instead of the diamine-type neutral chelating ligands used in the standard C-H borylation conditions. It is reported that the employment of these newly discovered catalysts show excellent reactivity and ortho-selectivity for diverse classes of aromatic substrates with high isolated yields. Moreover, the catalysts proved to be efficient for a wide number of aliphatic substrates for selective C(sp3)-H bond borylations. Heterocyclic molecules are selectively borylated using the inherently elevated reactivity of the C-H bonds. A number of late-stage C-H functionalization have been described using the same catalysts. Furthermore, we show that one of the catalysts could be used even in open air for the C(sp2)-H and C(sp3)-H borylations enabling the method more general. Preliminary mechanistic studies suggest that the active catalytic intermediate is the Ir(bis)boryl complex, and the attached ligand acts as bidentate ligand. Collectively, this study underlines the discovery of new class of C-H borylation catalysts that should find wide application in the context of C-H functionalization chemistry.
- Chattopadhyay, Buddhadeb,Hassan, Mirja Md Mahamudul,Hoque, Md Emdadul
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supporting information
p. 5022 - 5037
(2021/05/04)
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- Transient imine as a directing group for the metal-free o-C-H borylation of benzaldehydes
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Organoboron reagents are important synthetic intermediates and have wide applications in synthetic organic chemistry. The selective borylation strategies that are currently in use largely rely on the use of transition-metal catalysts. Hence, identifying much milder conditions for transition-metal-free borylation would be highly desirable. We herein present a unified strategy for the selective C-H borylation of electron-deficient benzaldehyde derivatives using a simple metal-free approach, utilizing an imine transient directing group. The strategy covers a wide spectrum of reactions and (i) even highly sterically hindered C-H bonds can be borylated smoothly, (ii) despite the presence of other potential directing groups, the reaction selectively occurs at the o-C-H bond of the benzaldehyde moiety, and (iii) natural products appended to benzaldehyde derivatives can also give the appropriate borylated products. Moreover, the efficacy of the protocol was confirmed by the fact that the reaction proceeds even in the presence of a series of external impurities.
- Rej, Supriya,Chatani, Naoto
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supporting information
p. 2920 - 2929
(2021/03/01)
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- Diastereodivergent [3 + 2] Annulation of Aromatic Aldimines with Alkenes via C-H Activation by Half-Sandwich Rare-Earth Catalysts
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Stereodivergent catalysis is of great importance, as it can allow efficient access to all possible stereoisomers of a given product with multiple stereocenters from the same set of starting materials. We report herein the first diastereodivergent [3 + 2]
- Cong, Xuefeng,Hou, Zhaomin,Mo, Zhenbo,Nishiura, Masayoshi,Zhan, Gu
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supporting information
p. 5531 - 5537
(2020/04/09)
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- Luminescent ruffled iridium(iii) porphyrin complexes containing N-heterocyclic carbene ligands: structures, spectroscopies and potent antitumor activities under dark and light irradiation conditions
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A panel of iridium(iii) porphyrin complexes containing axial N-heterocyclic carbene (NHC) ligand(s) were synthesized and characterized. X-ray crystal structures of the bis-NHC complexes [IrIII(ttp)(IMe)2]+ (2a), [IrIII(oep)(BIMe)2]+ (2d), [IrIII(oep)(IiPr)2]+ (2e) and [IrIII(F20tpp)(IMe)2]+ (2f) display ruffled porphyrin rings with mesocarbon displacements of 0.483-0.594 ? and long Ir-CNHC bonds of 2.100-2.152 ?. Variable-temperature 1H NMR analysis of 2a reveals that the macrocycle porphyrin ring inversion takes place in solution with an activation barrier of 40 ± 1 kJ mol?1. The UV-vis absorption spectra of IrIII(por)-NHC complexes display split Soret bands. TD-DFT calculations and resonance Raman experiments show that the higher-energy Soret band is derived from the 1MLCT dπ(Ir) → π*(por) transition. The near-infrared phosphorescence of IrIII(por)-NHC complexes from the porphyrin-based 3(π, π*) state features broad emission bands at 701-754 nm with low emission quantum yields and short lifetimes (Φem III(por)(IMe)2]+ complexes (por = ttp and oep) are efficient photosensitizers for 1O2 generation (Φso = 0.64 and 0.88) and are catalytically active in the light-induced aerobic oxidation of secondary amines and arylboronic acid. The bis-NHC complexes exhibit potent dark cytotoxicity towards a panel of cancer cells with IC50 values at submicromolar levels. The cytotoxicity of these complexes could be further enhanced upon light irradiation with IC50 values as low as nanomolar levels in association with the light-induced generation of reactive oxygen species (ROS). Bioimaging of [IrIII(oep)(IMe)2]+ (2c) treated cells indicates that this Ir complex mainly targets the endoplasmic reticulum. [IrIII(oep)(IMe)2]+ catalyzes the photoinduced generation of singlet oxygen and triggers protein oxidation, cell cycle arrest, apoptosis and the inhibition of angiogenesis. It also causes pronounced photoinduced inhibition of tumor growth in a mouse model of human cancer.
- Lam, Tsz-Lung,Tong, Ka-Chung,Yang, Chen,Kwong, Wai-Lun,Guan, Xiangguo,Li, Ming-De,Kar-Yan Lo, Vanessa,Lai-Fung Chan, Sharon,Lee Phillips, David,Lok, Chun-Nam,Che, Chi-Ming
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p. 293 - 309
(2019/01/04)
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- Structure-Reactivity Relationship in the Frustrated Lewis Pair (FLP)-Catalyzed Hydrogenation of Imines
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The autoinduced, frustrated Lewis pair (FLP)-catalyzed hydrogenation of 16-benzene-ring substituted N-benzylidene-tert-butylamines with B(2,6-F2C6H3)3 and molecular hydrogen was investigated by kinetic analysis. The pKa values for imines and for the corresponding amines were determined by quantum-mechanical methods and provided a direct proportional relationship. The correlation of the two rate constants k1 (simple catalytic cycle) and k2 (autoinduced catalytic cycle) with pKa difference between imine and amine pairs (ΔpKa) or Hammett's σ parameter served as useful parameters to establish a structure-reactivity relationship for the FLP-catalyzed hydrogenation of imines.
- Tussing, Sebastian,Kaupmees, Karl,Paradies, Jan
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supporting information
p. 7422 - 7426
(2016/05/24)
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- Synthesis of 2-Alkyl-3-aryloxaziridines
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A convenient method for the synthesis of 2-alkyl-3-aryloxaziridines 1 based on the formation of stable azomethines and their oxidation with m-chloroperoxybenzoic acid is reported.The scope and limitation of the method proposed is illustrated with numerous
- Kloc, Krystian,Kubicz, Elzbieta,Mlochowski, Jacek,Syper, Ludwik
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p. 1084 - 1087
(2007/10/02)
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