Journal of Chemical Research

The study of fluorescence quenching of 2-amino-7-bromofluorene (ABF) by chloromethanes (CH₂Cl₂, CHCl₃, CCl₄) in various solvents reveals that (i) the quenching constant k_q depends on solvent viscosity for CCl₄ and on solvent polarity for CH₂Cl₂ and CHCl₃; (ii) the observed positive deviation in methanol and acetonitrile in the Stern–Volmer plot is due to the presence of a static component in quenching; (iii) the fluorescence quenching is mainly due to the formation of a non-emissive charge transfer complex in the excited state.

The title reactions are an example of direct introduction of an aryl group into DNA bases.

Keggin type heteropolyacids supported on silica efficiently dehydrated secondary and tertiary alcohols under mild conditions and in good yields to afford the correspondent alkenes.

A set of four fulvenes bearing both electron-withdrawing and -donating aryl groups at C₆ was prepared and shown to be fairly stable, except for the dimerisation of the anisyl-nitrophenyl-fulvene 1a, which also underwent a (4π + 2π) cycloaddition with C,N-diphenylnitrone.

The role of linker chirality on the osmium catalysed asymmetric dihydroxylation of trans-stilbene has been examined using the ligand prepared from the C₂ symmetric chiral trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid 1 and dihydrocinchonine (+)-2. Whereas the ligand prepared using (11S,12S)-(-)-1 as linker with dihydrocinchonine gave the diol in 85% ee in the asymmetric dihydroxylation of trans-stilbene, the diol was obtained in 52% ee using the ligand prepared from the (11R,12R)-(+)-1.

The synthesis of three highly oxygenated, diastereomeric and optically active oxetanes from D-mannitol is described.

A simple and convenient procedure for the synthesis of sulfones from arenesulfonyl chlorides and alkyl halides using the Sm/HgCl₂ bimetallic system in tetrahydrofuran is presented.

Treatment of 3-tetrahydropyranyloxy-17α-aryl estradiols, dissolved in acetonitrile or acetonitrile/THF/pentane mixture, with trimethylsilyl iodide resulted in the soft deprotection of THP ether in good yields without side dehydratation.

7-selenodaunomycinone derivatives 3a–e were synthesised by condensation of daunomycinone 2 with aryl selenols catalysed by trifluoroacetic acid in dichloromethane at room temperature. When the concentration of aryl selenol exceeds 2 to 2–3 times, 7-deoxydaunomycinone 4 can be obtained. Also 7S-configuration of 3a can turn into 7R-isomer catalysed by boron trifluoride-etherate.

1-(β-hydroxyalkyl) benzotriazoles were prepared via reductive addition reactions of Bt¹CH₂SO₂Ph or Bt¹CH₂OC(O)Ph with aldehydes and ketones under mild conditions promoted by SmI₂.

Aryl schiff bases were efficiently reduced to the corresponding secondry amines by triethylammonium formate/formic acid system under microwave irradiation in solvent–free condition.

Trityl ethers are chemoselectively deprotected to the corresponding alcohols in high yields by a catalytic amount of indium tribromide in aqueous acetonitrile. The method is compatible with various functional groups such as acetonides, acetates, benzoates, olefins, carbamates, esters and ethers present in the substrate.

The dependence of the dissociation constants of oxalic acid on temperature and composition of ethylene glycol–water binary mixtures have been studied. Thermodynamic and extrathermodynamic analysis of the obtained results have been examined. The pK values have been correlated with the dielectric constant of the medium according to Born's electrostatic equation.

The alkyl group on the imino bridge of heterobifunctional reactive dyes plays a major role in improving the dyeing properties. The configurations of a pair of model compounds 2,4-dimethoxy-6-anilino-s-triazine and 2,4-dimethoxy-6-(N-metyl-anilino)-s-triazine have been determined by X-ray diffraction analysis of single crystals. The planar angle between the triazinyl and phenyl rings of the above models are 8.35° and 72.22° respectively. It indicates that the steric effect of the ethyl group produces a non-planar configuration and leads to the improvement of the dyeing properties.

The addition of dialkyl acetylenedicarboxylates to isatin, a strong NH acid, in the presence of triphenylphosphine leads to stable crystalline phosphorus ylids in excellent yields and one of the three synthesised compounds (3a) exists as a mixture of two rotational isomers on the basis of variable temperature nmr spectroscopy.

Reaction of 3-hydroxythiochromen-4-ones 1a,b with appropriate1-aryloxy-4-chlorobut-2-ynes 2a–f furnished 3-(4′-aryloxybut-2-ynyloxy)thiochromenones 3a–g in 80–90% yields. Substrates 3a–g on refluxing in chlorobenzene for 8–10 h gave 3-aryloxymethyl-2-methylfuro[3,2-b]-thiochromen-9-ones in 90–95% yields.

Condensation of 10b-methyl-1,5,6,10b-tetrahydroimidazo[2,1-a]isoquinolin-2(3H)-one with aromatic aldehydes affords 10b-(2-arylethenyl)-1,5,6,10b-tetrahydroimidazo[2,1-a]isoquinolin-2(3H)-one derivatives, which on heating in ethanol easily transform to 2,3,5,6-tetrahydropyrrolo[2,1-a]isoquinoline-3-carboxamides.

A one-pot synthesis of dialkyl 5-ethoxy-6-oxo-1,2-diphenyl-1,2,5,6-tetrahydro-pyridazine-3,4-dicarboxylates by reaction of ethyl 2-(1,2-diphenylhydrazino)-2-oxoacetate, dialkyl acetylenedicarboxylate, and triphenylphosphine in good yields is reported.

A revised synthesis of the antitumour antibiotic L-azatyrosine is reported, the main features of which are the unam-biguous synthesis of the previously misinterpreted 2-iodo-5-methoxypyridine and subsequent palladium-catalysed coupling with an iodoalanine-derived zinc reagent.

The synthesis of maritimin (1), a chromone from Pancratium maritimum L., is described

Gallium mediated allylation and cinnamylation reactions of 1,2-diones in presence of LiBr and KI afforded α-hydroxycarbonyl compounds in moderate to good yields.

Specific base-catalysed and unatalysed nucleophilic reactions of hydrazine with N-phthaloyl-glycine (NPG) have been observed in hydrazine buffers of pH 7.39–8.45. Cleavage of NPG in morpholine buffers of pH 8.25-9.16 shows only uncatalysed reaction between morpholine and NPG.