Nickel/Iridium Metallaphotoredox Catalysis for Allylic C-H Bond Arylation of -Allyl Heterocycles.

Despite conceptual breakthroughs in dual photoredox- and nickel-catalyzed arylation of radicals, the approach remains largely limited to localized C-centered radicals. Here, we extend it to allylic radicals, focusing on -allyl heterocycles. Using [Ir(dF(CF)ppy)(dtbbpy)]PF and NiCl(dtbbpy) under visible light, we achieve regioselective γ-amino radical arylation, yielding enamines in good yields.

Rhodium(i)-catalyzed cascade C(sp)-H bond alkylation - amidation of anilines: phosphorus as traceless directing group.

We introduce a versatile Rh(i)-catalyzed cascade reaction, combining C(sp)-H bond functionalization and amidation between -arylphosphanamines and acrylates. This innovative approach enables the rapid synthesis of dihydroquinolinone scaffolds, a common heterocycle found in various pharmaceuticals. Notably, the presence of the phosphorus atom facilitates the aniline -C(sp)-H bond activation prior to N-P bond hydrolysis, streamlining one-pot intramolecular amidation.

Merging C-H Bond Activation, Alkyne Insertion, and Rearrangements by Rh(III)-Catalysis: Oxindole Synthesis from Nitroarenes and Alkynes.

We report a Rh(III)-catalyzed -C-H bond functionalization of nitroarenes with 1,2-diarylalkynes and carboxylic anhydrides. The reaction unpredictably affords 3,3-disubstituted oxindoles with the formal reduction of the nitro group under redox-neutral conditions. Besides good functional group tolerance, this transformation allows the preparation of oxindoles with a quaternary carbon stereocenter using nonsymmetrical 1,2-diarylalkynes.

Upgrading Carbazolyl-Derived Phosphine Ligands Using Rh-Catalyzed P-Directed C-H Bond Alkylation for Catalytic CO-Fixation Reactions.

We report an Rh(I)-catalyzed C-H bond alkylation of PhenCarPhos [-(2-(diphenylphosphaneyl)phenyl)carbazole] and some congener phosphine ligands with alkenes. The C-H bond functionalization occurred exclusively at the C1 position of the carbazolyl unit because the trivalent phosphine acts as a directing group. This protocol provides straightforward access to a large library of C1-alkyl substituted PhenCarPhos, which outperformed common commercial or unfunctionalized phosphines and their precursors in the Pd-catalyzed carbon dioxide-fixation reactions with propargylic amines.

Photoinduced Arylation of Acridinium Salts: Tunable Photoredox Catalysts for C-O Bond Cleavage.

A photoinduced arylation of N-substituted acridinium salts has been developed and has exhibited a high functional group tolerance (e.g., halogen, nitrile, ketone, ester, and nitro).

Broadening of horizons in the synthesis of CD-labeled molecules.

In the light of the recent potentials of deuterated molecules as pharmaceuticals or even in mechanistic understanding, efficient methods for their synthesis are continually desired. CD-containing molecules are prominent amongst these motifs due to the parallel of the "magic methyl effect": introducing a methyl group into pharmaceuticals could positively affect biological activities. The trideuteromethyl group is bound to molecules either by C, N, O, or S atom.

Palladium-Catalyzed C-H Bond Arylation of Cyclometalated Difluorinated 2-Arylisoquinolinyl Iridium(III) Complexes.

The utility of C-H bond functionalization of metalated ligands for the elaboration of aryl-functionalized difluorinated-1-arylisoquinolinyl Ir(III) complexes has been explored. Bis[(3,5-difluorophenyl)isoquinolinyl](2,2,6,6-tetramethyl-3,5-heptanedionato) iridium(III) undergoes Pd-catalyzed C-H bond arylation with aryl bromides. The reaction regioselectively occurred at the C-H bond flanked by the two fluorine atoms of the difluoroaryl unit, and on both cyclometalated ligands.

C-H Bond Arylation of Pyrazoles at the β-Position: General Conditions and Computational Elucidation for a High Regioselectivity.

Direct arylation of most five-membered ring heterocycles are generally easily accessible and strongly favored at the α-position using classical palladium-catalysis. Conversely, regioselective functionalization of such heterocycles at the concurrent β-position remains currently very challenging. Herein, we report general conditions for regioselective direct arylation at the β-position of pyrazoles, while C-H α-position is free.

Access to functionalized luminescent Pt(ii) complexes by photoredox-catalyzed Minisci alkylation of 6-aryl-2,2'-bipyridines.

Photoredox-mediated C-H bond alkylation of 6-aryl-2,2'-bipyridines with N-(acyloxy)phthalimides is reported. The reaction exhibits excellent functional group tolerance, including chiral aliphatic groups. The influence of the incorporated C6'-alkyl group on the photophysical properties of the corresponding (N^N^C) cyclometalated Pt(ii) complexes is described, including chiroptical properties.

Exploiting the Reactivity of Fluorinated 2-Arylpyridines in Pd-Catalyzed C-H Bond Arylation for the Preparation of Bright Emitting Iridium(III) Complexes.

Pd-catalyzed C-H bond arylation applied to 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine () and 2-(3,5-difluorophenyl)-5-(trifluoromethyl)pyridine () allows the access to two families of Ir(III) complexes, charge-neutral and cationic species. The reaction is regioselective since only the C3- or C4-position of the fluorinated phenyl ring of or is readily functionalized - namely the C-H bond flanked by the two fluorine atoms which is the most acidic - which allows the electronic control of the reactive site. A range of electron-withdrawing (CN, COEt, C(O)Me) substituents on the aryl group has been incorporated leading to the pro-ligands (, Ar-2,4-dFppy; , Ar = -CH-CN; , Ar = -CH-COEt; , Ar = -CH-C(O)Me; , and Ar-3,5-dFppy; , Ar = -CH-COEt).

Late-Stage Diversification of Biarylphosphines through Rhodium(I)-Catalyzed C-H Bond Alkenylation with Internal Alkynes.

We report herein P(III)-directed C-H bond alkenylation of (dialkyl)- and (diaryl)biarylphosphines using internal alkynes. Chloride-free [Rh(OAc)(COD)] acts as a better catalyst than commercially available [RhCl(COD)]. Conditions were developed to control the mono- and difunctionalization depending on the alkyne stoichiometry.

Synthesis of 2-Arylpyridines and 2-Arylbipyridines via Photoredox-Induced Meerwein Arylation with in Situ Diazotization of Anilines.

We report herein a sustainable method for the preparation of 2-arylpyridines through C-H arylation of pyridines using in situ formed diazonium salts (from commercially available aromatic amines) in the presence of a photoredox catalyst under blue light-emitting diode (LED) irradiation. The reaction is tolerant to a wide range of functional groups (e.g.

Regioselective Pd-catalyzed direct C1- and C2-arylations of lilolidine for the access to 5,6-dihydropyrrolo[3,2,1-]quinoline derivatives.

The Pd-catalyzed C-H bond functionalization of lilolidine was investigated. The use of a palladium-diphosphine catalyst associated to acetate bases in DMA was found to promote the regioselective arylation at α-position of the nitrogen atom of lilolidine with a wide variety of aryl bromides. From these α-arylated lilolidines, a second arylation at the β-position gives the access to α,β-diarylated lilolidines containing two different aryl groups.

Rh -Catalyzed P -Directed C-H Bond Alkylation: Design of Multifunctional Phosphines for Carboxylation of Aryl Bromides with Carbon Dioxide.

We report the C-H alkylation of biarylphosphines at the ortho' position(s) with alkenes by using rhodium(I) catalysis, which provides straightforward access to a large library of multifunctionalized phosphines. Some of these modified ligands outperformed commercially available phosphines in the Pd-catalyzed carboxylation of aryl bromides with carbon dioxide in the presence of a photoredox catalyst.

Late-Stage Diversification of Imidazole-Based Pharmaceuticals through Pd-Catalyzed Regioselective C-H Bond Arylations.

Palladium-catalyzed C-H bond arylation of imidazoles has been applied to pharmaceuticals such as Bifonazole, Climbazole, and Prochloraz. In the presence of phosphine-free Pd(OAc) catalyst, aryl bromides are efficiently coupled at the C5-position of the imidazole units, which are widely decorated. Under these conditions, only C-H bond arylation reaction occurred without affecting the integrity of chemical structure of the imidazole-based pharmaceuticals.

Pd/C as Heterogeneous Catalyst for the Direct Arylation of (Poly)fluorobenzenes.

The potential of the heterogeneous catalyst 10 % Pd/C in the direct arylation of (poly)fluorobenzene derivatives with aryl bromides has been investigated. In general, high yields of biaryl derivatives were obtained by using tri-, tetra-, and pentafluorobenzenes, whereas mono- and difluorobenzenes exhibited poor reactivity. The regioselectivities of the arylation reactions were similar to those observed with homogeneous palladium catalysts.

Novel cyclometallated 5-π-delocalized donor-1,3-di(2-pyridyl)benzene platinum(ii) complexes with good second-order nonlinear optical properties.

Five new platinum(ii) complexes bearing a cyclometallated 5-π-delocalized donor-1,3-di(2-pyridyl)benzene were prepared and fully characterized. Their second-order nonlinear optical (NLO) properties were determined by the Electric-Field Induced Second Harmonic generation (EFISH) technique, working in DMF solution with an incident wavelength of 1907 nm, whereas the dipole moments were determined by Density Functional Theory (DFT) calculations. Remarkably, the platinum(ii) complex with a cyclometallated 5-guaiazulene-CH[double bond, length as m-dash]CH-1,3-di(2-pyridyl)benzene appears as a very good candidate for application in photonics, being characterized by the largest second-order NLO response.

Photoredox Catalysis for Building C-C Bonds from C(sp)-H Bonds.

Transition metal-catalyzed C-H bond functionalizations have been the focus of intensive research over the last decades for the formation of C-C bonds from unfunctionalized arenes, heteroarenes, alkenes. These direct transformations provide new approaches in synthesis with high atom- and step-economy compared to the traditional catalytic cross-coupling reactions. However, such methods still suffer from several limitations including functional group tolerance and the lack of regioselectivity.

Metal-free C(sp)-H bond sulfonyloxylation of 2-alkylpyridines and alkylnitrones.

Pyridin-2-ylmethyl tosylate derivatives are obtained in high yields from 2-alkylpyridine 1-oxides via a [3,3]-sigmatropic rearrangement of the adduct between 2-alkylpridine 1-oxides with benzenesulfonyl chlorides. Moreover, alkylnitrones also undergo [3,3]-sigmatropic rearrangement to give α-tosylated ketones after hydrolysis. Substitution reactions with nucleophiles then lead to diverse useful functionalizations for the synthesis of pincer ligands.

Halo-substituted benzenesulfonyls and benzenesulfinates: convenient sources of arenes in metal-catalyzed C-C bond formation reactions for the straightforward access to halo-substituted arenes.

Palladium-catalyzed reactions using aryl halides as one of the coupling partners represent a very popular method for generating carbon-carbon bonds. However, such couplings suffer from important limitations. As most palladium catalysts are very effective for the cleavage of C-halo bonds (Halo = Cl, Br or I), in many cases, the presence of several halide functional groups on arenes is not tolerated.

Late stage modifications of P-containing ligands using transition-metal-catalysed C-H bond functionalisation.

Phosphorus containing molecules have seen widespread applications in the development of innovative metal-ligand catalysts and materials. In recent years, the implementation of late-stage modifications of phosphorus derivatives via ortho-regioselective C-H bond functionalisation has led to faster and better ways for the synthesis of complex ligands by creating new reactions with low impact on the environment. This Feature article highlights transition-metal catalysed regioselective C-H bond functionalisation of phosphorus-containing molecules, in which the phosphorus containing unit plays the role of a directing group for C-H bond activation and the synthesis of new functional phosphorus derivatives.

Reactivity of bromoselenophenes in palladium-catalyzed direct arylations.

The reactivity of 2-bromo- and 2,5-dibromoselenophenes in Pd-catalyzed direct heteroarylation was investigated. From 2-bromoselenophene, only the most reactive heteroarenes could be employed to prepare 2-heteroarylated selenophenes; whereas, 2,5-dibromoselenophene generally gave 2,5-di(heteroarylated) selenophenes in high yields using both thiazole and thiophene derivatives. Moreover, sequential catalytic C2 heteroarylation, bromination, catalytic C5 arylation reactions allowed the synthesis of unsymmetrical 2,5-di(hetero)arylated selenophene derivatives in three steps from selenophene.

Reactivity of 1,2,3- and 1,2,4-Trifluorobenzenes in Palladium-Catalyzed Direct Arylation.

The higher reactivity of the C4-H bond as compared to the C5-H bond of 1,2,3-trifluorobenzene in palladium-catalyzed direct arylation allows the selective synthesis of 4-aryl-1,2,3-trifluorobenzenes in moderate to high yields. In most cases, phosphine-free Pd(OAc) catalyst and inexpensive KOAc base were employed. Then, from these 4-aryl-1,2,3-trifluorobenzenes, the palladium-catalyzed C-H bond functionalization of the C6-position allows the synthesis of the corresponding 4,6-diarylated 1,2,3-trifluorobenzenes.

Synthesis of 2-Pyridinemethyl Ester Derivatives from Aldehydes and 2-Alkylheterocycle N-Oxides via Copper-Catalyzed Tandem Oxidative Coupling-Rearrangement.

Successful benzylic C(sp)-H acyloxylation of 2-alkylpyridine, 2-alkylpyrazine, and 2-alkylthiazole compounds was achieved using simple aldehydes. This was carried out via a copper-catalyzed tandem reaction, involving oxidative esterification followed by O-atom transfer of the resultant high yield formed Boekelheide intermediate. The method enables the preparation of functional heterocycles and the desymmetrization of 2,6-dialkylpyridines for efficient synthesis of dissymmetric pincer ligands, thus offering a new life for more practical Boekelheide rearrangement.

Metal-Catalyzed C-H Bond Activation of 5-Membered Carbocyclic Rings: A Powerful Access to Azulene, Acenaphthylene and Fulvene Derivatives.

Azulene, acenaphthylene and fulvene derivatives exhibit important physical properties useful in materials chemistry as well as valuable biological properties. Since about two decades ago, the metal-catalyzed functionalization of such compounds, via C-H bond activation of their 5-membered carbocyclic ring, proved to be a very convenient method for the synthesis of a wide variety of azulene, acenaphthylene and fulvene derivatives. For such reactions, there is no need to prefunctionalize the 5-membered carbocyclic rings.