Studies of some monocyclic and bicyclic arylacetonitriles

The high-resolution (1)H, (13)C, (1)H-(1)H COSY and (1)H-(13)C COSY NMR spectra have been recorded in CDCl(3) for arylacetonitriles 1-12 and analyzed. The arylacetonitriles 3-7 exist in two isomeric forms E (methyl group is anti to cyano group) and Z (the methyl group is syn to cyano group) in solution. Normal chair conformation with equatorial orientations of phenyl rings at C-2 and C-6 for monocyclic nitriles 1 and 2, epimeric chair structure EC (axial configuration of methyl group at C-3) for both the E and Z isomers of arylacetonitrile derivatives (3-7) and a distorted boat form, B(3), for the N-acylacetonitrile derivatives (8-10) have been proposed based on NMR data. The bicyclic nitriles 11 and 12 exist in twin chair conformations in solution. DFT calculations and chemical shifts also support these conformations. Geometry optimizations for 1-12 were carried out according to density functional theory using B3LYP/6-31G(d,p) basis set and for 1 and 8 the theoretical geometrical parameters have been compared with those of single crystal measurements.     

Synthesis of medium-ring bicyclic bridgehead diamines from monocyclic diamines via α-aminoammonium ions

Condensation of 4-chlorobutanal and 5-chloropentanal with six cyclic diamines gave twelve α-aminoammonium salts; cleavage of these with LiAlH₄ gave medium-ring bicyclic diamines.     

A comparison of monocyclic and bicyclic phospholanes as acyl-transfer catalysts

The synthesis and evaluation of chiral phosphines 11, 15a, 19a, 24a, and 28a as nucleophilic catalysts for anhydride activation and kinetic resolution of alcohols is described. The relative reactivity follows the order 11a > 11b > 15a > 1 in the monocyclic series, and 24a > 19a > 28ain the bicyclic series, with an overall rate advantage of ca. 2 orders of magnitude for the bicyclic phospholanes over the monocyclic analogues. The increased reactivity of the bicyclic phospholanes for the acylation of alcohols is attributed to conformational effects and ground-state destabilization in a highly associative mechanism. Kinetic resolution data demonstrate promising enantioselectivities for 24a.     

Synthesis and spectroscopic properties of

The title compound has been synthesized as the first oligothiophenophane that has the typical stacking structure of a layered cyclophane and can behave as an ideal pi-dimer model.     

Synthesis and spectroscopic properties of N-azolylpropanamides

Fourteen N-azolylpropanamides have been prepared by Michael addition of azoles on acrylamide. The compounds have been fully characterized by IR and by ¹H and ¹³C-nmr. The isolated compounds are the most stable derivatives; kinetic compounds were observed but could not be isolated.     

Synthesis of oxepane ring containing monocyclic, conformationally restricted bicyclic and spirocyclic nucleosides from D-glucose: a cycloaddition approach

Carbohydrate-derived substrates having (i) C-5 nitrone and C-3-O-allyl, (ii) C-4 vinyl and a C-3-O-tethered nitrone, and (iii) C-5 nitrone and C-4-allyloxymethyl generated tetracyclic isoxazolidinooxepane/-pyran ring systems upon intramolecular nitrone cycloaddition reactions. Deprotection of the 1,2-acetonides of these derivatives followed by introduction of uracil base via Vorbrüggen reaction condition and cleavage of the isooxazolidine rings as well as of benzyl groups by transfer hydrogenolysis yielded an oxepane ring containing bicyclic and spirocyclic nucleosides. The corresponding oxepane based nucleoside analogues were prepared by cleavage of isoxazolidine and furanose rings, coupling of the generated amino functionalities with 5-amino-4,6-dichloropyrimidine, cyclization to purine rings, and finally aminolysis.     

Synthesis and properties of bicyclic aziridines,derivatives of triacetoneamine

Bicyclic aziridines, derivatives of 2,2,6,6-tetramethyl-4-piperidone (triacetoneamine), are synthesized, which by acids treatment undergo the N—C(1) or N—C(2) bonds cleavage to form the corresponding pyrrolines, pyrrolidines, and piperidines. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 508–511, March, 2007.     

Synthesis and spectroscopic properties of new bis-tetrazoles

Syntheses of N,N′-phenyltetrazole podands link with aliphatic chains containing oxygen, nitrogen and sulphur atoms, are described. The complexing properties of these compounds towards metal cations (Fe²⁺, Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺) were investigated by absorption and infrared spectroscopy. The UV–Vis titrations were performed to estimate the stability constant values of the respective complexes with Cu²⁺ ion. Changes in UV–Vis absorption spectra and IR spectra of compound 6 under various concentrations of Cu²⁺ ion in methanol suggest formation of very unstable complex. The structure of ligand 2 has been deduced by X-ray crystallography.     

Synthesis and properties of a new fluorescent bicyclic 4-N-carbamoyldeoxycytidine derivative

[reaction: see text] A bicyclic 4-N-carbamoyldeoxycytidine derivative (1, dC(hpp)) geometrically locked was synthesized as a new fluorescent nucleobase. The hybridization properties of oligodeoxynucleotides containing dC(hpp) were investigated by use of T(m) analysis. It was found that dC(hpp) forms stable base pairs not only with the complementary guanine base, but also with the adenine base. Interestingly, the fluorescence of dC(hpp) was suppressed only when a dC(hpp)-dG base pair was formed.     

Synthesis and spectroscopic properties of some dideuterated cyanopyridines

4‐Cyanopyridine‐2,6‐d₂ ( 5a‐2,6‐d₂ ), 3‐cyanopyridine‐2,6‐d₂ ( 5b‐2,6‐d₂ ), and 2‐cyanopyridine‐4,6‐d₂ ( 5c‐4,6‐d₂ ) were synthesized from the corresponding 2‐, 3‐ or 4‐pyridinecarboxylic acid N‐oxides. These dideuterated products were characterized by their mass and NMR spectra.     

Synthesis and spectroscopic properties of a hexapyrenylbenzene derivative

In this paper, we present a synthetic approach to the first hexapyrenylbenzene starting from 4,5,9,10-tetrahydropyrene. Absorption and fluorescence spectroscopic measurements show strong and red-shifted fluorescence both from locally excited pyrene states and from the excitonic manifold of the aggregate. [structure: see text]     

Syntheses and X-ray structures of monocyclic,bicyclic, and spirocyclic gallium and indium boraamidinates

The reactions of [Li(2)[PhB(N(t)Bu)(2)]](2) with GaCl(3) in various stoichiometries yield [Li(thf)(4)][PhB(mu-N(t)Bu)(2)GaCl(2) x GaCl(3)] (1), [PhB(mu-N(t)Bu)(2)GaCl](2) (2), and [mu-Li(OEt(2))[PhB(N(t)Bu)(2)]Ga] (3a), a series of complexes in which the three chloride ligands are successively replaced by the dianion [PhB(N(t)Bu)(2)](2-). The X-ray structures of 1, 2, and 3a show that the boraamidinate ligand adopts an N,N'-chelating mode. In the ion-separated complex 1, one of the nitrogen atoms is coordinated to a GaCl(3) molecule. The related indium complexes [mu-LiCl(thf)(2)][PhB(mu-N(t)Bu)(2)InCl](2) (4) and [mu-Li(OEt(2))[PhB(mu-N(t)Bu)(2)]In] (3b) were obtained in a similar manner. Complex 4 is the indium analogue of 2 with the incorporation of a bissolvated LiCl molecule. In 3a and 3b the spirocyclic [[PhB(mu-N(t)Bu)(2)](2)M](-) (M = Ga, In) anions are N,N'-chelated to the [Li(OEt(2))](+) counterion. Prolonged reactions result in the formation of [PhB(mu-N(t)Bu)(2)GaCl][(t)BuN(H)GaCl(2)] (5) and [[PhB(mu-N(t)Bu)(2)InCl][(t)BuN(H)InCl(2)][mu-LiCl(OEt(2))(2)]] (6), respectively. The X-ray structures of 5 and 6 reveal bicyclic structures which formally involve the entrapment of the monomers (t)BuN(H)MCl(2) by a four-membered BN(2)M ring (M = Ga, In). The synthesis and X-ray structure of Cl(2)Ga[mu-N(H)(t)Bu](2)GaCl(2) are also reported.     

A computational study of the mechanisms of the photoisomerization reactions of monocyclic and bicyclic olefins

The mechanisms of the photochemical isomerization reactions were investigated theoretically using a model system of cyclohexene (1), cycloheptene (2), norbornene (3), and two bicyclic olefins (4 and 5) using the CASSCF (six-electron/six-orbital active space) and MP2-CAS methods with the 6-311(d,p) basis set. The structures of the conical intersections, which play a decisive role in such photoisomerizations, were obtained. The intermediates and transition structures of the ground state were also calculated to assist in providing a qualitative explanation of the reaction pathways. Two photoreaction pathways were examined in the present work. The first can produce a photoproduct with an extra ring. The other can yield a photoproduct with a smaller ring with an external double bond. Both pathways involve cyclic carbene intermediates. Also, our model investigations suggest that both reaction pathways follow a similar photochemical pattern as follows: reactant → Franck-Condon region → conical intersection → cyclic carbene intermediate → transition state → photoproduct. Moreover, these two reaction pathways can compete with each other since the energetics of their conical intersection points are quite similar. Our present theoretical results agree with the available experimental observations.     

Synthesis of bicyclic gamma-ylidenetetronates

The bicyclic gamma-ylidenetetronate motif found in several Stemona alkaloids was prepared in a stereoselective manner by addition of lithium methyl tetronate to an alkoxy oxonium ion formed from a lactone. The corresponding mixed alkyl ketal obtained was subjected to a Lewis acid-base-promoted dealkoxylation reaction to deliver the desired products.     

Synthesis and spectroscopic properties of silica-dye-semiconductor nanocrystal hybrid particles

We prepared silica-dye-nanocrystal hybrid particles and studied the energy transfer from semiconductor nanocrystals (= donor) to organic dye molecules (= acceptor). Multishell CdSe/CdS/ZnS semiconductor nanocrystals were adsorbed onto monodisperse Sto?ber silica particles with an outer silica shell of thickness 2-23 nm containing organic dye molecules (Texas Red). The thickness of this dye layer has a strong effect on the energy transfer efficiency, which is explained by the increase in the number of dye molecules homogeneously distributed within the silica shell, in combination with an enhanced surface adsorption of nanocrystals with increasing dye amount. Our conclusions were underlined by comparison of the experimental results with numerically calculated FRET efficiencies and by control experiments confirming attractive interaction between the nanocrystals and Texas Red freely dissolved in solution.     

Synthesis and spectroscopic properties of highly water-soluble perylene derivatives

Most known perylene diimides are lipophilic, with few exceptions of hydrophilic derivatives. Even in the latter case, the compounds have limited water solubility and show a strong tendency to self-aggregation. In this paper we present the synthesis of four new perylene derivatives with three and four basic side chains, obtained by functionalizing the bay-area of perylene. These molecules show great solubility in aqueous media as hydrochlorides and their tendency to self-aggregate is remarkably reduced with respect to the previously synthesized two-chained perylene diimides. Their different spectroscopic properties in various solvents and conditions are reported and discussed.     

Synthesis and spectral properties of tetraphenoxysubstituted erbium phthalocyanines containing peripheral phenyl and cyclohexyl fragments

Russian Chemical Bulletin - The synthesis of peripherally and non-peripherally substituted erbium phthalocyanines with cyclohexylphenoxyl or phenylphenoxyl fragments by the template condensation of...     

Synthesis and spectroscopic properties of tin(II) alkoxides

Tin(II) alkoxides (Sn(OR)₂, R=CH₃, C₂H₅ and C₄H₉) were synthesized. I.R., H-NMR, mass and Mössbauer spectra are reported and discussed in terms of possible solid and solution state structures. The molecular weight of the butoxy compound is determined in methylene chloride solution and indicates a dimeric substance.     

Conformational properties of simple monocyclic conjugated enediynes

An investigation employing the AM1 semi-empirical SCF MO method to calculate structure optimization and conformational interconversion pathways for Z-cyclonona-3-ene-1,5-diyne (1), Z-cyclodeca-3-ene-l,5-diyne (2), and Z-cycloundeca-3-ene-1, 5-diyne (3) has been undertaken. The plane-symmetrical half-chair conformation of 1 is calculated to be 23.8 kJ mol⁻¹ more stable than the planar C_2v transition-state geometry. Compound 2 has two energy-minimum conformations with the twistboat (C₂) form being 31.1 kJ mol⁻¹ more stable than the twist (C₁) geometry. The calculated energy barrier for interconversion of C₂ and C₁ conformations is 37.4 kJ mol⁻¹. The unsymmetrical twist-boat form of 3 is calculated to be the most stable conformation. The twist-boat geometry can undergo two degenerate processes to achieve a time-averaged symmetry of C_2v.     

Synthesis, spectroscopic properties, and electropolymerization of azulene dyads

Four azulene dyads have been synthesized and studied by spectroscopic and electrochemical methods. A triarylamine, a boron-dipyrromethene (BDP or BODIPY), a porphyrin, and an isoalloxazine moiety have been linked to an extended π electron system at the 2-position of azulene, leading to the dyads 1-4, respectively. For the synthesis of 1-4, first 2-(4-ethynyl-phenyl)azulene (EPA) was prepared, which was further reacted with the halogenated chromophores by Pd-catalyzed cross-coupling reactions. The dyads 1-4 exhibit strong absorption bands in the visible range, which are dominated by the absorption spectra of the individual subchromophores. Fluorometric studies of 2-4 revealed that after excitation of the subchromophoric unit attached to the parent azulene moiety, quenching mainly through energy transfer to azulene is effective, whereas possible charge-transfer interactions play only a minor role. Potentiodynamic oxidation of the dyads 1-4 leads to the formation of polymer films, which are deposited at the electrode. The polymer film derived from 1 was further characterized by spectroelectrochemistry. During positive doping of poly-1, a strong absorption band appears at 13,200 cm(-1), which is typical for triarylamine radical cations. This band is overlapping with a broad absorption band in the low-energy region that might be caused by charge-transfer interactions within the polymer.