Synthesis of <Emphasis Type="Italic">S</Emphasis>-Aryl/Alkyl Thiolcarbonates from Disulfides and Chloroformates in the Presence of the Zn/AlCl<Subscript>3</Subscript> System

Summary. A simple, general, and high yielding method has been developed for the synthesis of S-aryl/alkyl-O-aryl/alkyl thiolcarbonates from various chloroformates and disulfides by reductive cleavage of the S–S bond with a Zn/AlCl₃ system in dry acetonitrile at 80°C.     

Iron powder and tin/tin chloride as new reducing agents of Meerwein arylation reaction with unexpected recycling to anilines

Abstract

Simple and rapid route for Meerwein arylation reaction using iron powder or a mixture of tin/tin chloride has been developed. In the presence of iron powder, different aryl diazonium salts reacted with methyl vinyl ketone, acrylates, and isopropenyl acetate. Production of oximes was detected as the main product with acrylates or in a mixture with β-aryl methyl ketones in the case of methyl vinyl ketone. The in situ produced HNO₂ from an excess of NaNO₂/HCl was trapped by alkyl aryl radical to form oximes in the E configuration form. The presence of tin/tin chloride mixture in the reaction of the aryl diazonium salts with methyl vinyl ketone produced Michael products along with β-aryl methyl ketones. The predicted α-aryl methyl ketones from the reaction of isopropenyl acetate with the diazotized anilines were obtained using iron or tin/tin chloride mixture.     

A facile and efficient method for synthesis of xanthone derivatives catalyzed by HBF4/SiO2 under solvent-free conditions

Abstract  

HBF₄/SiO₂ was used as an efficient, green, and inexpensive catalytic system for synthesis of 12-aryl or 12-alkyl-8,9,10,12-tetrahydro-11H-benzo[a]xanthen-11-one derivatives via a one-pot three-component reaction of aldehydes, 2-naphthol, and cyclic 1,3-dicarbonyl compounds. The reactions proceeded rapidly at 80 °C under solvent-free conditions and the desired products were obtained in good to excellent yields.     

SbCl3-catalyzed solvent-free Friedel–Crafts reaction of phenols with mandelic acids to 3-aryl benzofuran-2(3H)-ones: Synthesis of spirocyclic 2,3-dihydrobenzofuran-2-ones

A facile, SbCl₃-catalyzed, one-pot, tandem Friedel–Crafts/lactonization reaction of phenols and mandelic acids has been developed under solvent-free conditions to afford 3-aryl benzofuran-2(3H)-ones in good to high yields (52–90%). Additionally, the utility of 3-aryl benzofuran-2(3H)-ones is demonstrated by using them as precursors in the synthesis of a new class of spirocyclic benzofuran-2-ones using classical synthetic methodologies.     

γ-Al2O3/triflic acid as cooperative catalysts for the tandem Michael addition/carbocyclization: An easy access to 2-substituted pyrrolo[2,1-a]isoquinolines and 3-substituted pyrrolidine-2,5-diones

A tandem Michael addition/carbocyclization of 3,4-dimethoxyphenethyl maleimide with carbon and sulfur nucleophiles is accomplished via a relay catalysis using γ-Al₂O₃/TfOH binary system. The X-ray Photoelectron Spectroscopy (XPS) analysis of binary system indicates the presence of AlF₃, AlO(OH) species_. This approach provides an easy access to 2-aryl or 2-thio aryl pyrrolo[2,1-a]isoquinolines in good yields in a tandem fashion. With suitable ratio of γ-Al₂O₃/TfOH binary system, the Michael addition of N/C/S nucleophiles to N-benzyl maleimide is also achieved. A key to the success of these reactions would be the generation of AlF₃, AlO(OH) species from γ-Al₂O₃ and TfOH, which might have delineated the disadvantageous background reactions usually displayed by a strong Brønsted acid such as TfOH.     

Study on the Reaction of CIS-1-Acetyl-2-Aryl-6,6-Dimethyl-5,7-Dioxospiro-[2,5]-4,8-Octadiones with Methanol

Cis-l-acetyl-2-aryl-6,6-dimethyl-5,7-dioxo-spiro-[2,5]-4,8-octadiones 3a-d (X=p-CH₃, p-Cl, H, p-NO₂) reacted with anhydrous methanol in a sealed tube at 80°C to form trans, cis-α-carbomethoxy-β-(α′-methoxy-α′-aryl)-γ-methoxy-γ-methyl-γ-butyrolactones 4a-d and cis, cis-α-carbomethoxy-β-(α′-methoxy-α′-aryl)-γ-methoxy-γ-methyl-γ-butyrolactones 5a-d in good yield.     

Superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids: synthesis of quinolin-2(1H)-one derivatives

The superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids by Bronsted superacids (CF₃SO₃H, HSO₃F) or strong Lewis acids AlX₃ (X=Cl, Br) results in the formation of 4-aryl quinolin-2(1H)-ones in quantitative yields. The vinyl triflates or vinyl chlorides may be formed as additional reaction products. The investigated amides in reactions with benzene give 4,4-diaryl 3,4-dihydroquinolin-2-(1H)-ones under the superelectrophilic activation. 4-Aryl quinolin-2(1H)-ones in POCl₃ are converted into 4-aryl 2-chloroquinolines. 4-Fluorophenyl-4-phenyl 3,4-dihydroquinolin-2-(1H)-one give N-formylation products in a yield of 79% under the Vilsmeier–Haack reaction conditions.     

Palladium-Catalyzed Enantioselective Cacchi Reaction: Asymmetric Synthesis of Axially Chiral 2,3-Disubstituted Indoles

We report herein the first examples of a palladium-catalyzed enantioselective Cacchi reaction for the synthesis of indoles bearing a chiral C2-aryl axis. In the presence of a catalytic amount of Pd(OAc)₂ and (R,R)-QuinoxP* ligand, reaction of N-aryl(alkyl)sulfonyl-2-alkynylanilides with arylboronic acids under oxygen atmosphere afforded enantioenriched 2,3-disubstituted indoles in high yields and enantioselectivity. The indole ring is constructed de novo in this process and a complexation-induced chirality transfer is proposed to account for the observed enantioselectivity.     

Synthesis of the Novel Antidepressant (R)-(-)-Rolipram

Enantioselective synthesis of (R)-Rolipram 1 has been achieved through a conjugate addition of cyanide to enantiomerically pure 2-(2-aryl ethenyl)oxazoline 2, followed by selective reduction of the adduct with NaBH₄-NiCl₂.     

Bridge-Clamp Bis(tetrazine)s with [N]8 π-Stacking Interactions and Azido-s-Aryl Tetrazines: Two Classes of Doubly Clickable Tetrazines

Click chemistry at a tetrazine core is useful for bioorthogonal labeling and crosslinking. Introduced here are two new classes of doubly clickable s-aryl tetrazines synthesized by Cu-catalyzed cross-coupling. Homocoupling of o-brominated s-aryl tetrazines leads to bis(tetrazine)s structurally characterized by tetrazine cores arranged face-to-face. [N]₈ π-stacking interactions are essential to the conformation. Upon inverse electron demand Diels–Alder (iEDDA) cycloaddition, the bis(tetrazine)s produce a unique staple structure. The o-azidation of s-aryl tetrazines introduces a second proximal intermolecular clickable function that leads to double click chemistry opportunities. The stepwise introduction of fluorophores and then iEDDA cycloaddition, including bioconjugation to antibodies, was achieved on this class of tetrazines. This method extends to (thio)etherification, phosphination, trifluoromethylation and the introduction of various bioactive nitrogen-based heterocycles.     

Cobalt-Catalyzed Efficient Convergent Asymmetric Hydrogenation of E/Z-Enamides

Using the diphosphine-cobalt-zinc catalytic system, an efficient asymmetric hydrogenation of internal simple enamides has been realized. In particular, the Ph-BPE ligand can achieve convergent asymmetric hydrogenation of E/Z-substrates. High yields and excellent enantioselectivities were obtained for both acyclic and cyclic enamides bearing α-alkyl-β-aryl, α-aryl-β-aryl, and α-aryl-β-alkyl substituents. Hydrogenated products can be applied for the synthesis of useful chiral drugs such as Arfromoterol, Rotigotine, and Norsertraline. In addition, reasonable catalytic mechanism and stereocontrol mode are proposed based on DFT calculations.     

Coupling and cycloaddition of ynamides: homo- and Negishi coupling of tosylynamides and intramolecular [4+2] cycloaddition of N-(o-ethynyl)phenyl ynamides and arylynamides

N,N′-aryl- and N,N′-alkyl-buta-1,3-diyne-1,4-ditosylamides have been synthesized for the first time, in good to excellent yields, by copper-catalyzed dimerization of the corresponding N-aryl or N-alkyl tosylynamides. Negishi coupling of N-ethynylzinc tosylamides derivatives with (hetero)aryl iodides in the presence of Pd₂dba₃ and triphenylphosphine affords N-aryl and N-alkyl arylynamides in yields of up to 90%. Intramolecular [4+2] cycloaddition reactions of N-ethynylphenyl ynamides and arylynamides allow the synthesis of carbazoles and benzannulated and heteroannulated carbazoles in moderate-to-good yields.     

Cobalt-Catalyzed 1,4-Aryl Migration/Desulfonylation Cascade: Synthesis of α-Aryl Amides

A cobalt-catalyzed 1,4-aryl migration/disulfonylation cascade applied to α-bromo N-sulfonyl amides was developed. The reaction was highly chemoselective, allowing the preparation of α-aryl amides possessing a variety of functional groups. The method was used as the key step to synthesize an alkaloid, (±)-deoxyeseroline. Mechanistic investigations suggest a radical process.     

Triphenylphosphine: a catalyst for the synthesis of C-aryl furanosides from furanosyl halides

An array of C-aryl furanosides was prepared in good yields from furanosyl halides and aryl Grignard reagents in Et₂O using PPh₃ as a catalyst.     

2-Aryl propionamides via 1,4-aryl radical migration from N-arylsulfonyl-2-bromopropionamides

Reaction of N-alkyl-N-arylsulfonyl-2-halo-propionamides with pentamethyldiethylenetriamine and either CuBr or CuCl leads to 2-aryl propionamides via initial radical generation, 1,4-aryl migration with loss of SO₂ and reduction of the intermediate amidyl radical in 40-99% yields.     

Chemical Synthesis of N-Aryl Glycosides

Along with the O- and C-aryl glycosides, N-aryl glycosides represent an important class of carbohydrate and heterocyclic aryl conjugates that possess diverse applications and implications of biological interest. However, most of the synthetic efforts have been directed toward the preparation of O- and C-aryl glycosides. This review focuses on the various strategies that have been employed to synthesize N-aryl glycosides, most of which developed in the past 20 years. Besides having their unique applications, these N-aryl glycosides can also be treated as the analogs of O- and C-aryl glycosides. Wide ranges of reaction conditions are discussed for the optimum conditions.     

Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen: LXX. Erste Arylrheniumoxide (σ-Aryl)ReO3

The first examples of arylmetal oxides of general formula (σ-aryl)MO_x have been synthesized, for M = Re. The compounds (σ-aryl)ReO₃ (3) are obtained in a simple, ostensibly general route by treatment of dirhenium heptoxide with the corresponding arylzinc compound Zn(σ-aryl)₂. As side product, the zinc perrhenate Zn(thf)₂(ReO₄)₂ formed and precipitated as insoluble material from the solution. (Mesityltrioxo)rhenium(VII) was characterized by an X-ray diffraction study (pyramidal geometry).     

Five-membered 2,3-dioxo heterocycles: LXXXII. Recyclization of dimethyl 4,5-Dioxo-4,5-dihydro-1H-pyrrole-2,3-dicarboxylates in reaction with monosubstituted hydrazines. crystalline and molecular structure of dimethyl 1-benzyl-5-(4-methylphenylcarbamoyl)-1H-pyrazole-3,4-dicarboxylate

Dimethyl 1-aryl(benzyl)-4,5-dioxo-4,5-dihydro-1H-pyrrole-2,3-dicarboxylates reacted with phenylhydrazine and benzylhydrazine to give dimethyl 1-aryl(benzyl)-5-[(aryl or benzyl)carbamoyl]-1H-pyrazole-3,4-dicarboxylates.     

Synthesis of N 2-Arylisocytidines and N 2-Aryl-2′-deoxyisocytidines

2-(Arylamino)pyrimidin-4-ones were synthesized, silylated, and condensed with l,2,3,5-tetra-O-acetyl-β- d-ribofuranoside to afford the corresponding N ²-aryl protected isocytidines. Deprotection of the acetylated isocytidines using saturated NH₃ in MeOH solution gave 1-(β-d-ribofuranosyl)-2-(arylamino)-4-pyrimidinones. Methyl 2-deoxy-3,5-di-O-toluyl-α/β-d-ribofuranoside was prepared and condensed with the previously silylated bases to afford the anomeric mixture of protected nucleosides. The pure β-anomers were synthesized with better yield by treating the sodium salts of N ²-arylisocytosine derivatives with 2-deoxy-3,5-di-O-toluyl-α-d-ribofuranosyl chloride. Deprotection of the latter anomers afforded the corresponding free hydroxyl derivatives. The synthesized free nucleosides are under antiviral and oligonucleotide investigations.     

1,4-Aryl migration under copper(I) atom transfer conditions

Reaction of N-alkyl-N-(trichloroacetyl)arylsulfonamides with CuCl/amines leads to N-alkyl-N-(dichloroacetyl)-arylsulfonamides via reduction or N-alkyl-aryldichloroacetamides via 1,4-aryl migration with loss of SO₂. The ratio of reduction to aryl migration is dependent upon the temperature and the ligand utilised. Along with amide bond hydrolysis these reactions may compete when carrying out slow atom transfer radical cyclisation reactions using sulfonamides.