Volume 67, Issue 1

6-Allyloxypurines readily undergo palladium-catalysed Claisen rearrangement under mild conditions affording N 1-substituted hypoxanthines. In contrast with the previously reported protocol, the Claisen rearrangement can be performed using Pd(PPh3)4 or Pd(dba)2/dppf in dry THF at 60°C. The reaction can accommodate variously substituted allyl fragments to position N 1 of the hypoxanthine skeleton with high yields. Retention of the double bond configuration during rearrangement was observed.

Methyl methacrylate and styrene copolymers containing pendant benzil groups, such as 1-[4-(2-methacroyloxyethoxy)phenyl]-2-phenyl-1,2-ethanedione-co-methyl metacrylate (BzMA/MMA), 1-[4-(2-methacroyloxyethoxy)phenyl]-2-phenyl-1,2-ethanedione-co-styrene (BzMA/S), and 1-phenyl-2-(4-propenoylphenyl)-1,2-ethanedione-co-styrene (PCOCO/S), were prepared and used as precursors for photochemically generated pendant benzoyl peroxides. Decomposition of the pendant benzoyl peroxides was subsequently used in grafting processes. Either irradiation or a combination of irradiation with subsequent thermal treatment was adopted for grafting a thin layer of BzMA/MMA copolymer onto the surface of LDPE films. The grafting resulted in a significant decrease in contact angle of the film surface. The same activation strategy was successfully adopted to initiate the polymerisation of acrylic or methacrylic acids from the surface of styrene copolymer films containing the initiator precursor in the polymer side chains (BzMA/S and PCOCO/S). The successful surface grafting was proved by contact angles measurement as well as by infrared spectroscopic analysis.

New fluorescence dyes with an alkoxysilane moiety were synthesised by the condensation of 3-(triethoxysilyl)-1-propanamine (3-aminopropyltriethoxysilane) with 4,10-benzothioxanthene-3,1′-dicarboxylic acid anhydride (BTXA) and N,N-dimethylaminonaphthalene-1,8-dicarboxylic acid anhydride (DMANA), which was accompanied by the formation of an imidic bridge. The compounds N-(3-(triethoxysilyl)propyl)-thioxantheno[2,1,9-dej]isoquinoline-1,3-dione (BTX-S) and 4-(N′, N′-dimethyl)-N-(triethoxysilyl)propyl-1,8-naphthalene dicarboxylic acid imide (DMAN-S) were characterised by steady-state and time-resolved fluorescence spectroscopy in chloroform and ethanol. Both conjugates (BTX-S and DMAN-S) exhibited absorption and emission bands in the same region as the un-substituted BTXA and DMANA. An important Stokes shift was observed for DMAN-S in ethanol. A high fluorescence quantum yield was observed for BTX-S in both solvents and for DMAN-S in chloroform. In addition, the newly developed fluorescent silane dyes were covalently attached to the microscopic particles of layered silicates and on the surface of SiO2 wafers as a proof of concept for fluorescence particle (surface) visualisation. The surface wafer modification was precisely characterised by X-ray photoelectron spectroscopy (XPS). Successful covalent linkage onto the particles of layered silicates was proved by confocal laser scanning microscopy technique.

The paper presents a simple synthesis of substituted propargyl vinyl ethers and their subsequent thermally-initiated Claisen rearrangement leading to various 3-substituted homoallenyl aldehydes. Several methods, including Sonogashira coupling, base-promoted substitution on the triple bond by sodium amide or butyllithium, and the preparation of substituted propargyl alcohols, were used in the initial step. Phosphate-protected homoallenyl aldehyde hydrazone derivatives were synthesised and fully characterised. The stereochemistry of 9-anthracene carbaldehyde hydrazone, which, surprisingly, afforded both cis and trans isomers, was established using X-ray analysis.

This paper deals with the preparation of a variously substituted non-symmetrical azine set. The starting molecule for their preparation was a protected hydrazone. The protection was performed applying Zwierzak’s method. This procedure is based on the transfer of hydrazine to diethylhydrazidophosphate, which reacts with aldehydes to produce protected hydrazones. In the second step of the procedure, under the action of sodium hydride, the addition of another aldehyde affords non-symmetrical azines in the reaction with the protected hydrazine. The procedure was shown to be a useful and effective method. In this, the second part of our study, we present results devoted to the preparation and full identification of non-symmetrical azines.

Nitrones serve as starting materials for the synthesis of many heterocycles. Oxidation of secondary amines using hydrogen peroxide and the catalytic amount of methyltrioxorhenium in ionic liquids is a useful method for the preparation of nitrones. Ultrasonic irradiation and ionic liquids have a positive influence on the reaction. The nitrones required were isolated in good yields. Corresponding hydroxylamines, which can be easily oxidised to nitrones, often accompanied the main products. Methyltrioxorhenium in ionic liquids was re-used in several reaction cycles without any deteriorating effect on the course of the reaction.

The reaction of propanedioic acid, 2-diazo-1,3-bis(1,1-dimethylethyl) ester (di-tert-butyl diazomalonate) with a series of cyclopenta[b]thiophenes in the presence of catalytic rhodium acetate was studied. The resulting S—C ylides underwent a rearrangement to form a heterocycle with different topology; thialene, in very low yields. Experimental and spectral data for all compounds are provided.

Aminohydroxylation of prochiral divinylcarbinol and subsequent Pd(II)-catalysed oxy-/amidocarbonylation of aminopentenediols is reported. The method was applied to the preparation of useful building blocks for syntheses of cytotoxic jaspines and glycosidase inhibitor DLX-homologues. The key intermediates, tetrahydrofuranolactones (l-arabino-II) and pyrrolidinolactones (l-arabino-IX and l-xylo-IX), were prepared in a short 2-step sequence from divinylcarbinol.

The direct acylation of quercetin (I) with 3-chloro-2,2-dimethylpropanoyl chloride (II) gives a complex reaction mixture. The synthesis of different acylated quercetin with from mono- to tetra-O-substituted functions was achieved in a simple procedure wherein the yield of isomers depended on the stoichiometric ratio of reagents. The crude reaction mixtures were analysed (LC-MS) and compared with the isolated products. Unambiguous structural characterisation of isomeric quercetin derivatives was confirmed by NMR analysis. In addition, the quercetin dimer can be obtained in a high yield in the simple procedure. The anti-oxidant activity and aldose reductase inhibition of the compounds were screened with the aim of providing bi-functional remedies to treat diabetic complications and other diseases where oxidative stress and the polyol pathway are key etiological factors.

Total synthesis of the natural d-ribo-phytosphingosine I and its 2-epimer III in the protected form was achieved through a common strategy. The aza-Claisen rearrangement of allylic thiocyanate (Z)-V incorporated the new stereogenic centre with nitrogen and the subsequent Wittig olefination constructed a non-polar side chain. Hydrogenation, followed by removal of protecting groups, completed the syntheses of I and III.

Straightforward preparation of enantiomerically highly enriched N-substituted aroylalanines has been developed. This process involves the combination of crystallization-induced asymmetric transformation and a conjugate addition of N-nucleophiles to the corresponding aroylacrylic acids. Further transformations to 3,4-dichlorobenzoylalanine and aroyl-l-alanines via periodate oxidation and stereoselective reduction to N-substituted syn-4-aryl-4-hydroxy-2-aminobutanoic acids are also described.

2,2′-Diiodo-1,1′-binaphthalene undergoes a tandem Heck reaction with methyl acrylate to afford methyl 2-(7H-dibenzo[c,g]fluoren-7-ylidene)acetate. As a consequence, the target macrocyclic diazene with binaphthalene unit attached via acrylamide linker was prepared by the stepwise building of acrylamide at a binaphthalene moiety, including the Doebner modification of the Knoevenagel condensation, and completed by oxidative macrocyclisation of aniline end-groups. Despite being an equimolar mixture of monomer and dimer, it exhibited remarkable changes in CD spectra due to reversible (E/Z) isomerisation of N=N diazene bonds upon irradiation at 365/465 nm. Although the dimer isomerises from (E) to (Z) isomer 7.4 times faster than the monomer, the latter’s contribution to the change in ellipticity at 307 nm in the photostationary state is 2.4 times greater.

A series of novel monomethylated salts derived from linear benzobisthiazole was prepared. The push-pull attributes of these new compounds are represented by a quaternised azolium cycle as the acceptor part at one end of the structure and the dialkylamino- or diarylamino-substituted benzene ring as the donor part at the opposite end. Both moieties are connected by a conjugated linker consisting of one or two double bonds. Such dipolar structures are promising candidates for non-linear optical materials. The quantum-chemical indices describing linear and non-linear optical properties were obtained from semi-empirical calculations. The relationships between the chemical structure and non-linear optical properties of the cations studied were obtained. Effective conjugation was confirmed by measuring the optical properties in the UV-VIS region.

In this work, the effect of inter- and intramolecular interactions of reactants and products, reactants concentration as well as the solvent effect on the ratio of E and Z isomers of isatinphenylsemicarbazones in the reaction mixture is examined. Theoretical calculations proved that Z isomers are more stable than E isomers. Experimental results confirmed the noncovalent intermolecular donor-acceptor interactions of the reactants in the reaction mixture at concentrations above 0.1 mol L−1. The E/Z isomer ratio of isatin-3-(4-phenyl)semicarbazone (I) and N-methylisatin-3-(4-phenyl)semicarbazone (II) depends on the initial concentrations of 3-amino-1-phenylurea (phenylsemicarbazide; V) and 1H-indole-2,3-dione (isatin; III), or 3-methylindol-2,3(1H)-dion (3-methylisatin; IV), respectively. Both isomers exhibit high thermal stability. Thermal E-Z isomerization takes place at temperatures above 70°C in N,N-dimethylformamide.