Efficient RuIII-catalyzed synthesis of 9-aryl-9H-xanthene-3,6-diols as precursors to fluorones

Efficient condensation of resorcinol and various aromatic aldehydes in the presence of RuCl₃nH₂O as a homogeneous catalyst under reflux conditions was investigated.It was found that a very simple method afforded good to excellent yields of the desired products.     

Time resolved fluorescence of anthracene in mixed crystals at 2K

An optical Kerr shuttered spectrograph has been used to time resolve the spontaneous fluorescence of aromatic mixed crystal systems at low temperature with moderate resolution. Transient effects on the fluorescence of anthracene in naphthalene excited with 614 cm^?1 vibrational excess energy in ¹B_2u have been observed that may signal measurable vibrational relaxation pathways. A model consistent with these observations is presented: it implicates a strong interaction between the intramolecular Franck—Condon and non-Franck—Condon modes in the relaxation process for specific excitation in the region of large excess lattice energy. Examination of the fluorescence for several aromatic systems integrated over the interval 0 to 30 ps following excitation high in the S₁ vibrational manifold failed to reveal evidence of non-Boltzmann vibrational distributions, although other largely unexplained effects have been observed.     

Intramolecular Cyclization of 1-Benzyl-2-(nitromethylene)pyrrolidines in Triflic Acid

1-Benzyl-2-(nitromethylene)pyrrolidines in triflic acid undergo intramolecular cyclization to afford the corresponding 2,3-dihydro-1H-pyrrolo[1,2-b]isoquinolinium triflates and/or 10-amino-2,3-dihydro-1H-pyrrolo[1,2-b]isoquinolinium triflates, depending on the nature of the aromatic substituent. Structures of products and reaction mechanisms are discussed.     

Anionic cyclizations of aromatic ester dithioacetals with facially biased α,β-unsaturated ketones

Cyclopent-2-enones bearing a plane-nonsymmetric oxygen function on C-4 reacted efficiently with anions derived from aromatic ester dithioacetals to provide annulated products in a highly diastereoselective fashion. Whereas the anion of a dimethoxy aromatic ester dithiolane more rapidly reacted by an alternative intramolecular pathway, the anion of the corresponding aromatic ester dithiane was suitable for the intermolecular cyclization.     

Preparation of tripyrrane analogues from resorcinol and 2-methylresorcinol for applications in the synthesis of new benziporphyrin systems

Acid catalyzed condensation of resorcinol or 2-methylresorcinol with 2 equiv. of an acetoxymethylpyrrole gave bis(pyrrolylmethyl)benzene derivatives in moderate yields; these afforded a series of novel aromatic benziporphyrins using the MacDonald "3 + 1" methodology.     

Research in the chemistry of heterocyclic quinoneimines. 3. Oxidative cyclization of 2,5-diarylamino-substituted 1,4-benzoquinone-4-phenylimines — Simple method for the preparation of 2-arylamino-5-aryl-3-phenazinones

2,5-Diarylamino-1,4-benzoquinone-4-phenylimines, which are formed in the reaction of 1,4-benzoquinone-4-phenylimine with aromatic amines, are converted under oxidative conditions to products of intramolecular oxidative cyclization, viz., 2-arylamino-5-aryl-3-phenazinones.See [4] for Communication 2.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 330–333, March, 1984.     

Facile acid-catalyzed condensation of 2-hydroxy-2,2′-biindan-1,1′,3,3′-tetrone with phenols, methoxyaromatic systems and enols

Various phenols, methoxy aromatic compounds, 3- and 4-hydroxycoumarins and enols smoothly condense with 2-hydroxy-2,2′-biindan-1,1′,3,3′-tetrone 1 in an acid medium producing 2-aryl/alkyl-2,2′-biindan-1,1′,3,3′-tetrones in high yields. The adducts of resorcinol, 1,3,5-trihydroxybenzene and α- and β-naphthols of 1 preferably remain in the intramolecular hemi-ketal form, confirmed by X-ray diffraction studies. On the other hand para and meta substituted phenols condense with 1 in an acid medium to produce 6 or 7 substituted 2′,4-spiro(1′,3′-indanedion)-indeno[3,2-b]chromenes in good yields.     

聚醚砜激基缔合物的荧光光谱研究

本文研究了劳环在主链上的刚性高分子聚醚砜在二氯甲烷溶液中的荧光光谱.结果表明在适当的浓度下它也能形成分子间激基缔合物.     

Synthesis of 5-Amino-1-aryl-4-(4-aryl-1,3-thiazol-2-yl)- 2,3-dihydro-1H-pyrrol-3-ones*

Reactions of 2-(4-aryl-1,3-thiazol-2-yl)-3-oxo-4-chlorobutyronitriles with primary aromatic amines result in nucleophilic substitution of the chlorine atom by amino group, followed by intramolecular addition of the secondary amino group to the cyano group. The products are 5-amino-1-aryl-4-(4-aryl-1,3-thiazol-2-yl)- 2,3-dihydro-1H-pyrrol-3-ones which are structurally related to the known antiischemic drugs.     

On the mechanism of intramolecular sensitization of photocleavage of the 2-(2-nitrophenyl)propoxycarbonyl (NPPOC) protecting group

A spectroscopic study of a variety of covalently linked thioxanthone(TX)-linker-2-(2-nitrophenyl)propoxycarbonyl(NPPOC)-substrate conjugates is presented. Herein, the TX chromophore functions as an intramolecular sensitizer to the NPPOC moiety, a photolabile protecting group used in photolithographic DNA chip synthesis. The rate of electronic energy transfer between TX and NPPOC was quantified by means of stationary fluorescence as well as nanosecond and femtosecond time-resolved laser spectroscopy. A dual mechanism of triplet-triplet energy transfer has been observed comprising a slower mechanism involving the T1(pipi*) state of TX with linker-length-dependent time constants longer than 20 ns and a fast mechanism with linker-length-dependent time constants shorter than 3 ns. Evidence is provided that the latter mechanism is due to energy transfer from the T2(npi*) state which is in fast equilibrium with the fluorescent S1(pipi*) state. In the case of direct linkage between the aromatic rings of TX and NPPOC, the spectroscopic properties are indicative of one united chromophore which, however, still shows the typical NPPOC cleavage reaction triggered by intramolecular hydrogen atom transfer to the nitro group.     

Efficient synthesis of phosphorylated ortho-fused azaheterocycles

A simple and efficient two-step synthesis of various ortho-fused azaheterocycles, containing phosphorylated pyrimidinones as a parent component, was accomplished by the reaction of 2-diethoxyphosphoryl-3-methoxyacrylate with heteroaromatic amines followed by intramolecular N-acylation of the obtained substitution products. Optimization studies performed for the N-acylation reaction revealed that heating the addition products in Dowtherm A at 250 °C gave the best results. The same conditions applied in the intramolecular cyclization of ethyl 2-diethoxyphosphoryl-3-aminophenylacrylate gave expected product of the electrophilic aromatic substitution, but in low yield.     

多元酚的氰乙基和乙氧羰乙基化 I.

In the presence of alkoxide, resorcinol, methyl and nitro substituted resorcinol give C-polycyanoethyl-substituted products. When the 2-, 4- and 6-positions were occupied the O-cyanoethylation could occur. In the reaction of 2-nitroresorcinol with ethyl acrylate two β-carbethoxyethyl groups are introduced in a similar way to the 4-and 6-positions. The carbethoxyethylation products of resorcinol and 2-methylresorcinol lose ethyl alcohol during distillation giving the corresponding lactones.     

Molecular iodine: An efficient and environment-friendly catalyst for the synthesis of calix[4]resorcinarenes

Iodine catalyzes the cyclocondensation of various aldehydes with resorcinol to give tetrameric cyclic products, resorcinarenes. Through the reaction of resorcinol with aromatic aldehydes, the product is obtained as a mixture of two isomers, the all-cis isomer (rccc) and the cis-trans-trans isomer (rctt), whereas a single diastereomer, the all-cis, is formed with aliphatic aldehydes. Besides excellent isolated yields, the use of iodine makes this procedure simple, convenient, cost-effective and practical.     

A RuH(2)(CO)(PPh(3))(3)-catalyzed regioselective arylation of aromatic ketones with arylboronates via carbon-hydrogen bond cleavage

When the reaction of aromatic ketones with arylboronates (arylboronic acid esters) using RuH(2)(CO)(PPh(3))(3) (3) as a catalyst was conducted in toluene, the corresponding arylation product was obtained in moderate yields. In this case, a nearly equivalent amount of a benzyl alcohol derived from a reduction of an aromatic ketone was also formed. The use of aliphatic ketones, such as pinacolone and acetone, as an additive or a solvent dramatically suppressed the reduction of the aromatic ketones and, as a result, ortho-arylation products were obtained in high yield based on the aromatic ketones. In these reactions, the aliphatic ketone functioned as a scavenger of ortho-hydrogens of the aromatic ketones and the B(OR)(2) moiety of the arylboron compound (HB species). A variety of aromatic ketones, such as acetophenones, acetonaphthones, tetralones, and benzosuberone, could also be used in this coupling reaction. Several arylboronates containing electron-donating (NMe(2), OMe, and Me) and -withdrawing (CF(3) and F) groups were also applicable to this coupling reaction. Intermolecular competitive reaction using pivalophenone-d(0)() and -d(5) and intramolecular competitive reaction using pivalophenone-d(1) were carried out using 3 as a catalyst. The k(H)/k(D) value for the intermolecular competitive reaction was substantially different, compared with intramolecular competitive reaction. This strongly suggests the production of an intermediate where the ketone carbonyl is coordinated to the ruthenium involved in this catalytic reaction. (1)H and (11)B NMR studies using 2'-methylacetophenone, phenylboronate (2), and pinacolone (6) indicate that 6 functions effectively as a scavenger of the HB species.     

On the mechanism of proton-induced fluorescence quenching of aromatic compounds

The quenching mechanism in polar media has been studied by means of nanosecond time-resolved spectroscopy, fluorimelry, and measurements of isotope exchange. The fluorescence of aromatic compounds having an intramolecular charge-transfer structure is quenched effectively by protons and the proton-induced quenching is caused by electrophilic protonation at one of the carbon atoms of the aromatic ring.     

Synthesis of a new coumarin dye for pH independent staining of lysosomes

A novel coumarin analogue, synthesized from 2-formylcinnamic acid and resorcinol via acid catalyzed condensation and intramolecular rearrangement, is used for pH-independent staining of lysosome in live cells via lysosomal esterase mediated fluorogenic deacetylation.     

Intramolecular deactivation of substituted quinolinium cations. Time-resolved fluorescence and semi-empirical calculations

The fluorescence quenching of N-alkylated quinolinium ions with and without a sulfonato group at the chain end is investigated by measurement of their fluorescence lifetimes. The presence of the sulfonato group leads to a reduction of the fluorescence lifetime from 21.78 ± 0.12 ns for N-ethylquinolinium cation to 0.31 ± 0.05 ns for the sulfonatoethyl compound in CH₃CN. The high intramolecular quenching efficiency depends on the alkyl chain length in CH₃CN. However, in H₂O as solvent, there is no preferential quenching of fluorescence by the sulfonato group, which is strongly solvated. Semi-empirical calculations of sulfonatoalkylquinolinium betaines support the proposal of intramolecular ring formation as the cause of the strong quenching effects. The chain-length dependence of the fluorescence decay in CH₃CN is correlated with the different orientations of an interacting oxygen lone pair with the aromatic π system.     

Synthesis of 2-Azastilbene Derivatives with Intramolecular Charge Transfer

The condensation reaction of 2-cyanomethyl-5-nitropyridine with aromatic aldehydes has been carried out with the aim of preparing 2-azastilbene derivatives having intramolecular charge transfer. The yield of the condensation products can be increased if the reaction is carried out in the medium used for obtaining the starting 2-cyanomethyl-5-nitropyridine without separating or purifying it. The electronic absorption spectra of the compounds show a charge-transfer band, the energy of which increases and the intensity falls with lowering of the electron-donor properties of the substituent in the 4-position. Introduction of the heteroatom into the acceptor part when changing from the stilbene to the 2-azastilbene system is accompanied by a decrease in the energy and increase in the intensity of the charge-transfer electronic transition.     

Novel synthesis of desymmetrized resorcinol derivatives: aryl fluoride displacement on deactivated substrates

A short, high-yielding synthesis of differentially substituted resorcinol derivatives has been developed that utilizes 1,3-difluorobenzene as the starting material and employs sequential nucleophilic aromatic substitution (S(N)Ar) reactions to generate desymmetrized products. The scope and limitations of the second S(N)Ar reaction on the deactivated 1-alkoxy-3-fluorobenzene intermediates have been investigated. This methodology has also been employed in the synthesis of desymmetrized catechol derivatives from 1,2-difluorobenzene.     

INTER AND INTRAMOLECULAR INTERACTIONS OF PORPHYRINS WITH 5,5'-DITHIOBIS(2-NITROBENZOIC ACID)

meso-Tetraphenylporphyrin and its metal [zinc(II) and copper(II)] derivatives form both inter and intramolecular complexes with 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB). The nature of interaction is predominantly charge transfer (CT) in origin, with the porphyrin functioning as a II-donor and DTNB as an acceptor. Among the covalently linked intramolecular systems, the magnitude of CT interaction varies with the position (of one of the aryl groups of the porphyrin) to which DTNB is attached as ortho meta > para. Steady-state and time-resolved fluorescence studies revealed electron transfer to be the dominant pathway for the fluorescence quenching in these systems. Steady-state photolysis experiments probed using EPR and optical absorption studies have shown that electron transfer (from the excited singlet state of the porphyrin) to DTNB results in the formation of thiyl radical and production of free thiolate anion. It is found that the products of electrochemical reduction of covalently linked porphyrin-DTNB systems are different from those observed for the photochemical studies.