Direct arylation of arene and N-heteroarenes with diaryliodonium salts without the use of transition metal catalyst

Understanding and Exploitation of Neighboring Heteroatom Effect for the Mild N-Arylation of Heterocycles with Diaryliodonium Salts under Aqueous Conditions: A Theoretical and Experimental Mechanistic Study

The mechanism of arylation of N-heterocycles with unsymmetric diaryliodonium salts is elucidated. The fast and efficient N-arylation reaction is interpreted in terms of the bifunctionality of the substrate: The consecutive actions of properly oriented Lewis base and Brønsted acid centers in sufficient proximity result in the fast and efficient N-arylation. The mechanistic picture points to a promising synthetic strategy where suitably positioned nucleophilic and acidic centers enable functionalization, and it is tested experimentally.

Selective Targeting of Heme Protein in Cytochrome P450 and Nitric Oxide Synthase by Diphenyleneiodonium

Cytochrome P450 (CYP) enzymes mediate mixed-function oxidation reactions important in drug metabolism. The aromatic heterocyclic cation, diphenyleneiodonium (DPI), binds flavin in cytochrome P450 reductase and inhibits CYP-mediated activity. DPI also inhibits CYP by directly interacting with heme. Herein, we report that DPI effectively inhibits a number of CYP-related monooxygenase reactions including NADPH oxidase, a microsomal enzyme activity that generates hydrogen peroxide in the absence of metabolizing substrates. Inhibition of monooxygenase by DPI was time and concentration dependent with IC50's ranging from 0.06 to 1.9 μM. Higher (4.6-23.9 μM), but not lower (0.06-1.9 μM), concentrations of DPI inhibited electron flow via cytochrome P450 reductase, as measured by its ability to reduce cytochrome c and mediate quinone redox cycling. Similar results were observed with inducible nitric oxide synthase (iNOS), an enzyme containing a C-terminal reductase domain homologous to cytochrome P450 reductase that mediates reduction of cytochrome c, and an N-terminal heme-thiolate oxygenase domain mediating nitric oxide production. Significantly greater concentrations of DPI were required to inhibit cytochrome c reduction by iNOS (IC50 = 3.5 µM) than nitric oxide production (IC50 = 0.16 µM). Difference spectra of liver microsomes, recombinant CYPs, and iNOS demonstrated that DPI altered heme-carbon monoxide interactions. In the presence of NADPH, DPI treatment of microsomes and iNOS yielded a type II spectral shift. These data indicate that DPI interacts with both flavin and heme in CYPs and iNOS. Increased sensitivity for inhibition of CYP-mediated metabolism and nitric oxide production by iNOS indicates that DPI targets heme moieties within the enzymes.

Organocatalytic Asymmetric Synthesis of Dihydrobenzoxazinones Bearing Trifluoromethylated Quaternary Stereocenters

Chiral phosphoric acid-catalyzed enantioselective aza-Friedel-Crafts reaction of trifluoromethyl benzoxazinones with pyrroles is reported. Under mild conditions, a range of enantioenriched dihydrobenzoxazinones bearing trifluoromethylated quaternary stereocenters could be obtained in good to excellent yield and ee. A remarkable fluorine effect is observed, and preliminary mechanistic studies combined with theory calculations suggest that triple-hydrogen-bonding interactions hold the transition structure rigidly and allow the bulky substituents of the catalyst to influence the enantioselectivity.

Metal-Free Direct α-Selective Arylation of Boron Dipyrromethenes via Base-Mediated C-H Functionalization

A metal-free direct α-selective arylation of BODIPYs has been developed based on base-mediated C-H functionalization with easily accessible diaryliodonium salts, which provides a straightforward facile access to a variety of α-arylBODIPY dyes. The α-regioselectivity was confirmed by X-ray analysis, and was studied by DFT calculation. The resultant dyes show strong absorption and emission over a broad range of spectra tunable via the simple variation of the diaryliodonium salts.

Pd(II)-Catalyzed C3-Selective Arylation of Pyridine with (Hetero)arenes

Palladium catalyzed, nondirected C3-selective arylation of pyridines with arenes and heteroarenes in the presence of 1,10-phenanthroline as the ligand has been developed. The optimized conditions allow for a highly C3-selective arylation of pyridines, affording various 3,3'-bipyridines and 3-arylpyridines.

Iron-catalyzed synthesis of arylsulfinates through radical coupling reaction

A novel iron-catalyzed synthesis of arylsulfinates from diaryliodonium salts and rongalite through radical coupling reaction is described. Desired products can be prepared in good yields in air at room temperature in 20 minutes without the need for any ligands and additives.

Arylation with Diaryliodonium Salts

This chapter focuses on recent developments in metal-free and metal-catalyzed arylations with diaryliodonium salts (diaryl-λ3-iodanes). Synthetic routes to diaryliodonium salts are briefly described, and chemoselectivity trends with unsymmetric iodonium salts are discussed.

An Alternative Synthetic Approach to 3-Alkylated/Arylated 5-Nitropyridines

An alternative method for the synthesis of 3-alkylated/arylated 5-nitropyridines was developed involving a three-component ring transformation of 3,5-dinitro-2-pyridone on treatment with aldehyde in the presence of ammonium acetate. This method facilitates the modification of the substituent at the 3-position by changing the precursor aldehyde. The use of solid ammonium acetate instead of ammonia as the nitrogen source renders the synthetic method more practical and user-friendly.

Iminoiodane- and Brønsted base-mediated cross dehydrogenative coupling of cyclic ethers with 1,3-dicarbonyl compounds

A one-pot, two-step approach to prepare 2-tetrahydrofuran and -pyran substituted 1,3-dicarbonyl compounds by PhI=NTs-mediated amination/Brønsted base-catalyzed cross dehydrogenative coupling (CDC) reaction of the cyclic ether and 1,3-dicarbonyl derivative under mild conditions is reported. The reaction is compatible with a variety of cyclic ethers and 1,3-dicarbonyl compounds, affording the corresponding coupled products in moderate to good yields of up to 80% over two steps.

Base promoted direct C4-arylation of 4-substituted-pyrazolin-5-ones with diaryliodonium salts

A metal-free approach for the C4-arylation of 4-substituted-pyrazolin-5-ones with diaryliodonium salts was developed.

Metal-free one-pot sequential direct diarylation of pyrazolin-5-ones with diaryliodonium salts

A novel and efficient one-pot sequential C4-diarylation of pyrazolin-5-ones with diaryliodonium salts at room temperature in the absence of a metal catalyst was reported.

Arylation with unsymmetrical diaryliodonium salts: a chemoselectivity study

Phenols, anilines, and malonates have been arylated under metal-free conditions with twelve aryl(phenyl)iodonium salts in a systematic chemoselectivity study. A new "anti-ortho effect" has been identified in the arylation of malonates. Several "dummy groups" have been found that give complete chemoselectivity in the transfer of the phenyl moiety, irrespective of the nucleophile. An aryl exchange in the diaryliodonium salts has been observed under certain arylation conditions. DFT calculations have been performed to investigate the reaction mechanism and to elucidate the origins of the observed selectivities. These results are expected to facilitate the design of chiral diaryliodonium salts and the development of catalytic arylation reactions that are based on these sustainable and metal-free reagents.

Development of a palladium-catalyzed decarboxylative cross-coupling of (2-azaaryl)carboxylates with aryl halides

A catalytic method for the decarboxylative coupling of 2-(azaaryl)carboxylates with aryl halides is described. The decarboxylative cross-coupling presented is mediated by a system catalytic in both palladium and copper without requiring stoichiometric amounts of organometallic reagents or organoboronic acids. This method circumvents additional synthetic steps required to prepare 2-azaaryl organometallics and organoborates as nucleophilic coupling partners, which are prone to protodemetallation and protodeborylation and produce potentially toxic byproducts.

Palladium-catalyzed arylation of simple arenes with iodonium salts

The development of an arylation protocol for simple arenes with diaryliodonium salts using the Herrmann-Beller palladacycle catalyst is reported. The reaction takes simple aromatic feedstocks and creates valuable biaryls for use in all sectors of the chemical industry.