Reactions Catalysed by a Binuclear Copper Complex: Relay Aerobic Oxidation of N -Aryl Tetrahydroisoquinolines to Dihydroisoquinolones with a Vitamin B1 Analogue

Photoredox Catalyzed Tandem Denitrogenative [4 + 2] Annulation of 1,2,3-Benzotriazin-4(3H)-ones with Terminal Olefins

The dihydroisoquinolones skeleton is ubiquitous in natural products and biological molecules. Reported strategies for constructing dihydroisoquinolones usually require noble metal catalysts or stoichiometric oxidants, which limit their wide applications. Herein, we developed a photoredox catalyzed tandem denitrogenative [4 + 2] annulation reaction of 1,2,3-benzotriazin-4(3H)-ones with terminal olefins. A variety of dihydroisoquinolones can be accessed in moderate to excellent yield. This protocol features high atom-economy, mild reaction conditions, and is external oxidant-free, enabling the synthesis of various substituted dihydroisoquinolones.

Triazine-Carbazole-Based Covalent Organic Frameworks as Efficient Heterogeneous Photocatalysts for the Oxidation of N-aryltetrahydroisoquinolines

Covalent organic frameworks (COFs) have attracted growing interests as new material platform for a range of applications. In this study, a triazine-carbazole-based covalent organic framework (COF-TCZ) was designed as highly porous material with conjugated donor-acceptor networks, and feasibly synthesized by the Schiff condensation of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tr ianiline (TAPB) and 9-(4-formylphenyl)-9H-carbazole-3,6-dicarbaldehyde (CZTA) under the solvothermal condition. Considering the effect of linkage, the imine-linked COF-TCZ was further oxidized to obtain an amide-linked covalent organic framework (COF-TCZ-O). The as-synthesized COFs show high crystallinity, good thermal and chemical stability, and excellent photoactive properties. Two π-conjugated triazine-carbazole-based COFs with tunable linkages are beneficial for light-harvesting capacity and charge separation efficiency, which are empolyed as photocatalysts for the oxidation reaction of N-aryltetrahydroisoquinoline. The COFs catalyst systems exhibit the outstanding photocatalytic performance with high conversion, photostability and recyclability. Photoelectrochemical tests were employed to examine the behavior of photogenerated charge carriers in photo-illumination system. The control experiments provide further insights into the nature of photocatalysis. In addition, the current research also provided a valuable approach for developing photofunctional COFs to meet challenge in achieving the great potential of COFs materials in organic conversion.

Efficient and scalable synthesis of 3,4-dihydroisoquinolin-1(2H)-ones by benzylic oxidation of tetrahydroisoquinoline derivatives using cerium ammonium nitrate (CAN)

An efficient and scalable method for the synthesis of 3,4-dihydroisoquinolin-1(2H)-ones through benzylic oxidation of tetrahydroisoquinoline derivatives using a catalytic amount of cerium ammonium nitrate (CAN) and a stoichiometric amount of NaBrO3 as oxidants was developed. The reaction is significantly influenced by the substituent groups on the phenyl ring. While electron-withdrawing groups on the phenyl ring can lower the reactivities of the substrates, electron-donating groups on the phenyl ring can dramatically promote the oxidation rate.

Diruthenium Tetracarboxylate-Catalyzed Enantioselective Cyclopropanation with Aryldiazoacetates

A series of chiral bowl-shaped diruthenium(II,III) tetracarboxylate catalysts were prepared and evaluated in asymmetric cyclopropanations with donor/acceptor carbenes derived from aryldiazoacetates. The diruthenium catalysts self-assembled to generate C4-symmetric bowl-shaped structures in an analogous manner to their dirhodium counterparts. The optimum catalyst was found to be Ru2(S-TPPTTL)4·BArF [S-TPPTTL = (S)-2-(1,3-dioxo-4,5,6,7-tetraphenylisoindolin-2-yl)-3,3-dimethylbutanoate, BArF = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate], which resulted in the cyclopropanation of a range of substrates in up to 94% ee. Synthesis and evaluation of first-row transition-metal congeners [Cu(II/II) and Co(II/II)] invariably resulted in catalysts that afforded little to no asymmetric induction. Computational studies indicate that the carbene complexes of these dicopper and dicobalt complexes, unlike the dirhodium and diruthenium systems, are prone to the loss of carboxylate ligands, which would destroy the bowl-shaped structure critical for asymmetric induction.

Oxidative α-Functionalization of 1,2,3,4-Tetrahydroisoquinolines Catalyzed by a Magnetically Recoverable Copper Nanocatalyst. Application in the Aza-Henry Reaction and the Synthesis of 3,4-Dihydroisoquinolones

The oxidative α-functionalization of 2-aryl-1,2,3,4-tetrahydroisoquinolines (THIQs) promoted by a versatile heterogeneous nanocatalyst consisting of copper nanoparticles immobilized on silica-coated maghemite (CuNPs/MagSilica) has been accomplished. The methodology was successfully applied in the cross-dehydrogenative coupling (CDC) reaction of N-aryl THIQs and other tertiary amines with nitromethane as a pro-nucleophile (aza-Henry reaction) and the α-oxidation of THIQs with O₂ as a green oxidant. Phosphite, alkyne, or indole derivatives were also shown to be suitable candidates for their use as pro-nucleophiles in the CDC reaction with THIQs. The catalyst, with very low copper loading (0.4-1.0 mol % Cu), could be easily recovered by means of an external magnet and reused in four cycles without significant loss of activity.

Visible Light Driven Metal-Free Photoredox Catalyzed α-benzylation and α-oxygenation of N-substituted tetrahydroisoquinolines: Applications to Synthesis of Natural Products

Herein, visible light mediated organophoto redox catalysed simple and convenient method for the a-benzylation and a-oxygenation of tertiary amines is demonstrated. Synthesis of novel thiophenol based donor acceptor organophotoredox catalysts 4a - 4d were investigated along with commercial catalyst 4-CzIPN ( 4e ). A diverse biologically active a-benzylated tetrahydroisoquinolines and natural products such as (±)-Norlaudanosine, (±)-laudanosine and (±)-xylopinine have been synthesized under the optimized conditions in yields ranging from from 62-91%. Exploitation of synthesized a-benzylated compound using present phtoredox catalyzed conditions gave rise to dehydyrogenative benzylic oxidation product under oxygen atmosphere which is known to display biologically and structurally important properties. Also, various N-protected tertiary amines were found to be suitable for the a-oxygenation reactions using catalyst 4e and resulted in good yields (61-85%).

Iron(III)-catalyzed α-cyanation and carbonylation with 2-pyridylacetonitrile: divergent synthesis of α-amino nitriles and tetrahydroisoquinolinones

Iron-catalyzed oxidative synthesis of N-aryl-substituted tetrahydroisoquinolines (THIQs) toward tetrahydroisoquinoline-based derivatives is reported. A wide range of α-amino nitriles and tetrahydroisoquinolinones are synthesized in moderate to good yields. This approach involves a new organic nitrile source, a cheap iron catalyst under an oxygen atmosphere, and temperature-controlled divergent synthesis and features complete selectivity and operational simplicity.

Chemical Recycling of Polystyrene to Valuable Chemicals via Selective Acid-Catalyzed Aerobic Oxidation under Visible Light

Chemical recycling is one of the most promising technologies that could contribute to circular economy targets by providing solutions to plastic waste; however, it is still at an early stage of development. In this work, we describe the first light-driven, acid-catalyzed protocol for chemical recycling of polystyrene waste to valuable chemicals under 1 bar of O₂. Requiring no photosensitizers and only mild reaction conditions, the protocol is operationally simple and has also been demonstrated in a flow system. Electron paramagnetic resonance (EPR) investigations and density functional theory (DFT) calculations indicate that singlet oxygen is involved as the reactive oxygen species in this degradation process, which abstracts a hydrogen atom from a tertiary C–H bond, leading to hydroperoxidation and subsequent C–C bond cracking events via a radical process. Notably, our study indicates that an adduct of polystyrene and an acid catalyst might be formed in situ, which could act as a photosensitizer to initiate the formation of singlet oxygen. In addition, the oxidized polystyrene polymer may play a role in the production of singlet oxygen under light.

Direct, Site-Selective and Redox-Neutral α-C-H Bond Functionalization of Tetrahydrofurans via Quantum Dots Photocatalysis

As one of the most ubiquitous bulk reagents available, the intrinsic chemical inertness of tetrahydrofuran (THF) makes direct and site-selective C(sp³ )-H bond activation difficult, especially under redox neutral condition. Here, we demonstrate that semiconductor quantum dots (QDs) can activate α-C-H bond of THF via forming QDs/THF conjugates. Under visible light irradiation, the resultant alkoxyalkyl radical directly engages in radical cross-coupling with α-amino radical from amino C-H bonds or radical addition with alkene or phenylacetylene, respectively. In contrast to stoichiometric oxidant or hydrogen atom transfer reagents required in previous studies, the scalable benchtop approach can execute α-C-H bond activation of THF only by a QD photocatalyst under redox-neutral condition, thus providing a broad of value added chemicals starting from bulk THFs reagent.

α-Oxygenation of N-aryl/alkyl heterocyclic compounds via ruthenium photocatalysis

We herein report ruthenium(iii) photocatalyzed oxidation of N-aryl tertiary amines to the corresponding amides.

Vitamin B1-catalyzed aerobic oxidative esterification of aromatic aldehydes with alcohols

A straightforward aerobic oxidative esterification of aryl aldehydes with alcohols has been developed for the synthesis of substituted esters by employing vitamin B1 as a cost-effective, metal-free, and eco-friendly NHC catalyst. Air is used as a green terminal oxidant. The reaction is a useful addition to the existing NHC-catalytic oxidative esterification.

An aerobic oxidative esterification of aryl aldehydes with alcohols has been developed by employing vitamin B1 as a cost-effective, metal-free, and eco-friendly NHC catalyst.

Thiyl radical promoted iron-catalyzed-selective oxidation of benzylic sp3 C–H bonds with molecular oxygen

A ligand-free iron-catalyzed method for the oxygenation of benzylic sp³ C–H bonds by molecular oxygen (1 atm) using a thiyl radical as a cocatalyst has been developed.

Atropisomerism in a 10-Membered Ring with Multiple Chirality Axes: (3 Z,9 Z)-1,2,5,8-Dithiadiazecine-6,7(5 H,8 H)-dione Series

For the first time, chirality in (3 Z,9 Z)-1,2,5,8-dithiadiazecine-6,7(5 H,8 H)-dione series was recognized. Enantiomers of the 4,9-dimethyl-5,8-diphenyl analogue were isolated at room temperature, and their thermal stability was determined. X-ray crystallography confirmed the occurrence of a pair of enantiomers in the crystal. Absolute configurations were assigned by comparing experimental and calculated vibrational/electronic circular dichroism spectra of isolated enantiomers. A distorted tesseract (four-dimensional hypercube) was used to visualize the calculated enantiomerization process, which requires the rotation around four chirality axes. Conformers of higher energy as well as several concurrent pathways of similar energies were revealed.

Crystal structure of tetra-kis-[μ-2-(meth-oxy-carbon-yl)benzoato-κ2O1:O1']bis-[(N,N-di-methyl-formamide-κO)copper(II)](Cu-Cu) di-methyl-formamide disolvate

The title compound, [Cu2(C9H7O4)4(C3H7NO)2]·2C3H7NO, crystallizes in the monoclinic P21/c space group, with the binuclear copper unit occupying a special position on an inversion center, i.e. the asymmetric unit of the crystal consists of one CuII ion, two 2-(meth-oxy-carbon-yl)benzoate ligands, and two DMF mol-ecules (one coordinated and one solvate). The binuclear complex displays a paddle-wheel-shaped structure with the two copper atoms being in a Jahn-Teller-distorted octa-hedral coordination environment. Each 2-(meth-oxy-carbon-yl)benzoate substituent acts as a bridging ligand and links two Cu atoms with a Cu-Cu distance of 2.633 (1) Å. The carboxyl-ate groups of the 2-(meth-oxy-carbon-yl)benzoate ligands adopt bidentate syn-syn bridging modes, with dihedral angles between the carboxyl-ate planes and the aromatic rings of 18.427 (4) and 43.029 (6)°. In the crystal, adjacent DMF mol-ecules coordinated to copper atoms are arranged in a mutual 'head-to-tail' manner by offset face-to-face π-π stacking inter-actions, resulting in chains along the c-axis direction. The planes of the coordinated DMF mol-ecules are parallel to each other, the distance between them being 3.33 (1) Å. A three-dimensional structure is assembled from the chains by weak C-H⋯O and C-H⋯π inter-molecular inter-actions involving the DMF solvent mol-ecules. One of the methyl ester groups is disordered over two sites with an occupancy ratio of 0.751 (12):0.249 (12).

Reactions catalyzed by a binuclear copper complex: selective oxidation of alkenes to carbonyls with O2

A binuclear copper complex bearing a simple salicylate ligand catalyses the efficient cleavage of styrenes into ketones and aldehydes with O₂ as the oxidant. The reaction works under an atmosphere of O₂ (balloon) with 0.5 mol% of catalyst and could be performed on a gram scale, providing an alternative to ozonolysis.