Journal of Chemical Research

Stable nitroxyl radicals are important tools in chemistry, biophysics, biology, and materials science. Their stability and the sensitivity of their EPR spectra to the local environment make them valuable molecular probes. This review seeks to give an overview of the developments in the field of nitroxide spin probes and their various applications, with the main focus on the pH-sensitive imidazoline nitroxide family.

Microwave irradiation has been used to accelerate the conversion of isatin (1a) and 5-nitroisatin (1b) into their Schiff bases 3-[5’-aryl(alkyl)-2’,4’-dihydro-1’,2’,4’-triazol-3’-on-4’-yl]iminoisatin (3a–g) and 3-[5’-aryl(alkyl)-2’,4’-dihydro-1’,2’,4’-triazol-3’-on-4’-yl]imino-5-nitroisatin (4a–g), respectively. Reaction was achieved by microwave-induced technique, which reduced the reaction time drastically and improved the yield when compared to conventional heating. The newly synthesised bases showed moderate antimicrobial activity against the standard bacterial and fungal organisms tested

Benzyltriphenylphosphonium nitrate in the presence of AlCl₃ oxidised 1,2,4-triazolidine-3,5-diones to the corresponding 4-substituted-1,2,4-triazole-3,5-diones.

Bis(cyclohexylmethyl) 3,6-bis(4-chlorophenyl)-1,2,4,5-tetrazine-1,2-dicarboxylate was prepared from cyclohexylmethyl chloroformate and 3,6-bis(4-chlorophenyl)-1,2(or 1,4)-dihydro-1,2,4,5-tetrazine and its structure was determined by X-ray diffraction. This reaction yields the title compound rather than bis(cyclohexylmethyl) 3,6-bis(4-chlorophenyl)-1,2,4,5-tetrazine-1,4-dicarboxylate. The 2,3-diazabutadiene group in the central six-membered ring of tetrazine is not planar and the tetrazine ring has a twist conformation.

A simple efficient method for the synthesis of new ferrocene bis thiocarbazones via microwave irradiation under solvent-free conditions has been developed. Compared to the conventional method, its major advantages are short reaction times, good conversions and actually accorded the green synthesis technology. The structures of target compounds were confirmed by ¹H NMR, IR, ESI-MS spectra data and elemental analysis. Preliminary bioassay results showed that some of these compounds possess inhibitory effects against S. aureus, S. pyogenes and E. coli bacteria.

Two novel triazine-based dendrimers comprising a dithienylethene core and eight and 16 ethyl groups around the periphery were synthesised in high yields in a convergent way, without using tedious protection and chromatographic separation steps. Their optical properties such as photochromism, fluorescence emission and film-forming behaviour were investigated. The new symmetrical dendritic dithienylethenes showed typical photochromic behaviour in solution and good film-forming performance in a poly(methyl methacrylate) (PMMA) matrix. Moreover, the dendrimers have demonstrated remarkable fluorescence enhancement and good solubility in common organic solvents, compared with the corresponding small molecule diarylethene. Thus, the new dendrimers as optoelectronic materials, have potential applications in optical storage, photo-switches, and so on.

Ditellurides undergo facile cleavage on treatment with rongalite (sodium hydroxymethanesulfinate) to generate tellurium anions in situ, which undergo ring opening of epoxides in high regioselective manner. A simple, cost-effective method has been developed to prepare β-hydroxytellurides with good yields.

An efficient preparation of hydroxysteroids by a one-pot, simultaneously rapid deprotection of 3-acyloxy groups and reduction of D-ring ketones (nitrile) of steroids using DIBAL-H in the presence of NiCl₂ (10 mol %) is described. The attractive features of this procedure for the preparation of the hydroxysteroid derivatives are the mild reaction conditions, short reaction time, excellent yields, clean reaction profiles, and an inexpensive catalyst system.

BaCl₂ dispersed on a nano-structural type of silica gel (BaCl₂-nano SiO₂) was found to be an effective catalyst for the rapid and high yielding preparation of substituted 2,4,6-triarylpyridine frameworks by the reaction of various acetophenones, benzaldehydes and ammonium acetate. The prepared catalyst was characterised by X-ray diffraction and scanning electron microscopy analysis.

Secondary or tertiary amides have been prepared directly from aryl, heteroaryl methyl ketones using an iodine– amine–NaOH system which afforded the expected products in good yields in an aqueous medium. The present method has the advantages of using inexpensive reagents, mild reaction condition and ease of manipulation.

Knoevenagel reaction of 2-cyanoacetylpyrrole with aromatic aldehydes afforded 2-(3-aryl-2-cyanopropenoyl)-1-methylpyrrole in 81–94% yields in ethanol catalysed by KF/Al₂O₃ under microwave irradiation. This method has the advantages of simplicity, good yields and low costs.

Treatment of N-phenyl-p-phenylenediamine and two equivalents of aniline with potassium dichromate in hot water acidified with a small amount of sulfuric acid gives 3-phenylamino-5-phenyl-7-aminophenazinium sulfate (pseudo-mauveine). The oxidation of N-phenyl-p-phenylenediamine and o-toluidine with potassium dichromate in water with a small amount of sulfuric acid gives 3-phenylamino-5-(o-toluyl)-7-amino-8-methylphenazinium sulfate. Oxidation of aniline and (o or p) toluidine only gave small quantities of mauveine chromophores. Oxidation of p-toluidine gives a known dimer which gives a purple coloured solution in acid. A hypothesis is described in which N-phenyl-p-phenylenediamine may have been involved in mauveine synthesis in the nineteenth century.

A one-pot, three-component reaction of an aldehyde, benzyl carbamate and allyltrimethylsilane in the presence of 3 mol% of magnesium bistrifluoromethanesulfonimide at room temperature has been shown to afford the corresponding protected homoallylic amine in high yield.

Seven novel pleuromutilin derivatives with thiazole-5-carboxamide and thioether moiety in the C₁₄ side chain were designed and synthesised. The antibacterial activities of the target compounds were tested via agar-well diffusion method in vitro. The results showed that three target compounds still had antibacterial activity against Staphylococcus aureus ATCC26112 and Staphylococcus aureus SC at a low concentration of 0.05 μg mL⁻¹.