Ultrasound-assisted thiocyanation of aromatic and heteroaromatic compounds using ammonium thiocyanate and DDQ

Thiocyanation of various aromatic and heteroaromatic compounds has been achieved in the presence of ammonium thiocyanate (NH(4)SCN) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in methanol solution under ultrasound irradiation. An ultrasonic probe of 24 kHz frequency has been used for this study. Whereas the use of ultrasound increases the rate of reactions compared with reactions at reflux conditions, the electron-donor ability of aromatic nucleus enhances also the rate of reaction.     

Lewis Acid Promoted Reactions. (IV.)1a,b Oxidation Deprotection of Trimethylsilyl Ethers with Silver and Sodium Bromates; AgBrO3, NaBrO3

Primary and secondary benzylic and saturated trimethylsilyl ethers are converted to their carbonyl compounds with AgBrO₃/AlCl₃ efficiently. p-Hydroquinonetrimethylsilyl ether is also converted with both AgBrO₃/AlCl₃ and NaBrO₃/AlCl₃ to p-benzoquinone. AgBrO₃/AlCl₃ is also able to oxidize primary trimethylsilyl ethers to their carboxylic acids. Primary and secondary benzylic trimethylsilyl ethers are also converted to their carbonyl compounds with NaBrO₃/AlCl₃; AgBrO₃ is more efficient and selective oxidant than NaBrO₃.     

Sonocatalytic oxidation of olefins catalyzed by heteropolyanion–montmorillonite nanocomposite

A Keggin-type heteropolyanion compound (HPO) was doped within the montmorillonite (MMT) structure by impregnation method. The synthesized catalyst was characterized by FT-IR, XRD, UV–vis, CV, SEM and elemental analysis. Based on chemical adsorption between HPO, and hydroxyl surface groups, HPOs nanoparticles were successfully located on the MMT. Moreover, the obtained nanocomposite was found as an efficient catalyst for oxidation of hydrocarbons under reflux and ultrasonic irradiation conditions.     

An Efficient and Selective Solid State Oxidation of Thiols to Disulfides with Quinolinium Fluorochromate on Silica Gel

Summary. Various kinds of aliphatic (cyclic and acyclic), aromatic, and heterocyclic thiols are converted into the corresponding disulfides by quinolinium fluorochromate (QFC) on silica-gel in excellent yields. Selective oxidation of thiols in the presence of sulfides is also achieved under solid phase conditions.     

Novel and chemoselective dehydrogenation of 2-substituted imidazolines with potassium permanganate supported on silica gel

Various types of 2-imidazolines are efficiently oxidized to the corresponding imidazoles using potassium permanganate supported on silica gel under mild conditions at room temperature. 2-Alkylimidazolines are selectively converted to their corresponding imidazoles in the presence of 2-arylimidazolines. Chemoselective oxidation of 2-imidazolines in the presence of other oxidizable functional groups such as sulfide, ether, aldehyde, acetal, and THP ether was also achieved by this reagent system.     

Dodecatungstocobaltate heteropolyanion encapsulation into MIL‐101(Cr) metal–organic framework scaffold provides a highly efficient heterogeneous catalyst for methanolysis of epoxides

A heterogeneous catalyst was synthesized by encapsulation of a Keggin‐type heteropolytungstate, potassium dodecatungstocobaltate trihydrate, K₅[CoW₁₂O₄₀]·(Co‐POM), into chromium(III) terephthalate (MIL‐101). Encapsulation was achieved via a ‘build bottle around ship’ strategy in aqueous media, following a hydrothermal method. The structure of the resulting crystalline solid was characterized using X‐ray diffraction, correlated with Fourier transform infrared and UV–visible spectroscopy. The metal content was analysed using optical emission spectroscopy. Transmission electron microscopy was used to measure particle size and N₂ adsorption in a Brunauer–Emmett–Teller instrument to characterize the specific surface area. The catalytic activity was investigated using methanolysis of epoxides under mild conditions as a test reaction. The turnover frequency of the heterogeneous Co‐POM@MIL‐101 catalyst was more than 20 times higher than that of the homogeneous Co‐POM catalyst. The Co‐POM@MIL‐101 catalyst was reused several times with negligible leaching of Co‐POM and with no considerable loss of its initial efficiency. The simplicity of preparation, extraordinary stability and high reactivity make Co‐POM@MIL‐101 an exceptional catalytic matrix that is easily separable from reaction media.     

Ultrasound promoted selective synthesis of 2-aryl-5,6-dihydro-4H-1,3-oxazines catalyzed by K-10 and KSF montmorillonite clays: A practical procedure under mild and solvent-free conditions

Montmorillonite K-10 and KSF were found to be highly efficient, environmentally friendly and recyclable heterogeneous catalysts for the selective synthesis of a variety of 2-aryl-5,6-dihydro-4H-1,3-oxazines from arylnitriles and 3-amino-1-propanol under ultrasound irradiation. This new methodology provides excellent yields in short reaction times (10–25 min). The reaction work-up is very simple and the catalysts can be easily separated from the reaction mixture and reused several times in subsequent reactions. This catalytic system also exhibits excellent chemoselectivity in the synthesis of mono-oxazines from dinitriles.     

N2O4/SiO2 system as an efficient reagent for rapid and chemoselective conversion of trimethylsilyl ethers to the parent alcohols under nonaqueous conditions

N₂O₄ was easily impregnated on silica gel to give a stable heterogeneous reagent N₂O₄/SiO₂ (I). Chemoselective deprotection of trimethylsilyl ethers to the corresponding alcohols was achieved in the presence of I in CH₂Cl₂ in excellent yields. The stability, easy preparation and high selectivity of the reagent make this method as a useful procedure for the selective deprotection of TMS ethers at room temperature.     

Silica sulfuric acid catalyzed synthesis of benzoxazoles,benzimidazoles and oxazolo[4,5-<Emphasis Type="Italic">b</Emphasis>]pyridines under heterogeneous and solvent-free conditions

A simple, rapid and efficient method for the preparation of benzoxazoles, benzimidazoles and oxazolo[4,5-b]pyridines from the reaction of orthoesters with o-aminophenols, o-phenylenediamine and 2-amino-3-hydroxypyridine in the presence of silica sulfuric acid under heterogeneous and solvent-free conditions is reported. The significant features of this method are short reaction times, high yields of the products, mild reaction conditions, solvent free reaction, cheapness, non-toxicity and reusability of the catalyst.     

Copper containing nanosilica thioalated dendritic material: A recyclable catalyst for synthesis of benzimidazoles and benzothiazoles

In this paper, the design and characterization of a new heterogeneous catalyst by incorporation of copper ions into the nanosilica modified by thiole–based dendrimer are reported. The prepared catalyst was characterized by FT–IR, TGA, elemental analysis, FE–SEM, TEM, XPS and ICP–OES techniques. This material was used as catalyst in the synthesis benzimidazoles and benzothiazoles by the reaction of substituted benzaldehydes with 1,2–diaminobenzene or 2–aminothiophenol, respectively. The advantages of the present catalytic system are high yields, mild conditions and short reaction times. On the other hand, this new synthesized catalyst was recycled very well and reused several times without significant loss of its catalytic activity.