Phenanthrenequinone-Sensitized Photocatalytic Synthesis of Polysubstituted Quinolines from 2-Vinylarylimines

Visible-light-excited 9,10-phenanthrenequinone (PQ*) was used as a photocatalyst for the synthesis of polysubstituted quinolines via the electrocyclization of 2-vinylarylimines. Up to quantitative yields of 2,4-disubstituted quinolines were received after 1 h of excitation with blue LEDs at room temperature when MgCO3 was used as an additive in DCM. On the basis of experimental and DFT studies, we propose that PQ* induces one-electron oxidation of the imine substrate that triggers the electrocyclization mechanism.Peer reviewe

Dual H-bond activation of NHC-Au(I)-Cl complexes with amide functionalized side-arms assisted by H-bond donor substrates or acid additives

Novel approach with amide-tethered H-bond donor NHC ligands enabled Au(I)-catalysis via H-bonding. The plain NHC-Au(I)-Cl complex catalysed conversions of terminal N-propynamides to oxazolines, and enyne cycloisomerization with an acid additive, in DCM at RT. DFT calculations enlightened the function of the side-arm in the activation.Novel approach with amide-tethered H-bond donor NHC ligandsenabled Au(I)-catalysisviaH-bonding. The plain NHC–Au(I)–Clcomplex catalysed conversions of terminalN-propynamides tooxazolines, and enyne cycloisomerization with an acid additive, inDCM at RT. DFT calculations enlightened the function of the side-arm in the activation.Peer reviewe

Biomimetic zinc chlorin-poly(4-vinylpyridine) assemblies : doping level dependent emission-absorption regimes

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Electron-Deficient Phenanthrenequinone Derivative for Photoactivated Hydrogen Atom Transfer Mediated Oxidation of Secondary Alcohols

In 2000, Fukuzumi and co-workers reported a seminal study on the photochemical oxidation of benzylic alcohols with visible-light-excited 9,10-phenanthrenequinone (PQ) under argon atmosphere (J. Am. Chem. Soc. 2000, 122, 8435). We optimized the reaction conditions they reported and were able to oxidize 1-(4-methoxyphenyl)ethanol quantitatively to 4'-methoxyacetophenone in only 15 min with 10 mol % PQ as a photocatalyst under oxygen. However, we observed a significant decrease in the oxidation rate with more electron-deficient benzylic alcohols as starting materials. To improve the photooxidation performance, we designed a high-yielding synthetic route for a novel, more electron-deficient PQ derivative, 3,6-bis(trifluoromethyl)-9,10-phenanthrenequinone (PQ-CF3). Its efficiency as a photocatalyst in the fast oxidation of secondary alcohols was demonstrated not only with several electronically diverse benzylic alcohols but also with aliphatic substrates. The comprehensive mechanistic studies based on Hammett plot construction, kinetic isotope experiments, and DFT computations suggest that the mechanistic pathway of the alcohol oxidation is dependent on the electronic properties of both the catalyst and the substrate. As the key mechanistic discovery, we showed that the newly developed PQ-CF3 operates as a highly efficient hydrogen atom transfer (HAT) catalyst.Peer reviewe

Carbocatalytic Oxidative Dehydrogenative Couplings of (Hetero)Aryls by Oxidized Multi‐Walled Carbon Nanotubes in Liquid Phase

HNO3-oxidized carbon nanotubes catalyze oxidative dehydrogenative (ODH) carbon-carbon bond formation between electron-rich (hetero)aryls with O-2 as a terminal oxidant. The recyclable carbocatalytic method provides a convenient and an operationally easy synthetic protocol for accessing various benzofused homodimers, biaryls, triphenylenes, and related benzofused heteroaryls that are highly useful frameworks for material chemistry applications. Carbonyls/quinones are the catalytically active site of the carbocatalyst as indicated by model compounds and titration experiments. Further investigations of the reaction mechanism with a combination of experimental and DFT methods support the competing nature of acid-catalyzed and radical cationic ODHs, and indicate that both mechanisms operate with the current material.Peer reviewe

Chlorophyll tailored 20-trifluoroacetamide and its azacrown derivative as pH sensitive colorimetric sensor probe with response to AcO-, F- and CN- ions

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Carbocatalytic Cascade Synthesis of Polysubstituted Quinolines from Aldehydes and 2-Vinyl Anilines

Oxidized active carbon (oAC) catalyses the formation of polysubstituted quinolines from o-vinyl anilines and aldehydes. The reaction proceeds in a cascade manner through condensation, electrocyclization and dehydrogenation, and gives access to a wide range of quinolines with alkyl and/or aryl substituents as demonstrated with 40 examples. The metal-free catalytic procedure allows a heterogeneous protocol for the synthesis of various polysubstituted quinolines. The mechanistic studies imply that both the acid and quinoidic groups in oAC are integral for the catalytic manifold.Peer reviewe

Visible-Light-Photocatalyzed Reductions of N-Heterocyclic Nitroaryls to Anilines Utilizing Ascorbic Acid Reductant

A photoreductive protocol utilizing [Ru-(bpy)3]2+ photocatalyst, blue light LEDs, and ascorbic acid(AscH2) has been developed to reduce nitro N-heteroaryls to the corresponding anilines. Based on experimental and computational results and previous studies, we propose that the reaction proceeds via proton-coupled electron transfer between AscH2, photocatalyst, and the nitro N-heteroaryl. The method offers a green catalytic procedure to reduce, e.g., 4-/8-nitroquinolines to the corresponding aminoquinolines, substructures present in important antimalarial drugs.A photoreductive protocol utilizing [Ru(bpy)(3)](2+) photocatalyst, blue light LEDs, and ascorbic acid (AscH(2)) has been developed to reduce nitro N-heteroaryls to the corresponding anilines. Based on experimental and computational results and previous studies, we propose that the reaction proceeds via proton-coupled electron transfer between AscH(2), photocatalyst, and the nitro N-heteroaryl. The method offers a green catalytic procedure to reduce, e.g., 4-/8-nitroquinolines to the corresponding aminoquinolines, substructures present in important antimalarial drugs.Peer reviewe