Organic luminophore 2-(biphenyl-4-yl)-5-phenyl-1,3,4-oxadiazole (PBD, III) was converted by series of reaction into thioamide VIII which cyclized with substituted bromoacetylarenes X to give the bifluorophore system XI. The thiazole analog XIII was obtained by analogous reaction of bromoacetyl derivative V with thiobenzamide. All the thus-prepared compounds exhibit pronounced fluorescence in solution as well as in the crystalline state.

The Friedel-Crafts acylation of 2-(biphenyl-4-yl)-5-phenyl-1,3,4-oxadiazole (PBD) with hippuryl chloride has been used to prepare the derivative V which on cyclization with POCl3 or P4S10 gives the respective oxazole (or thiazole) derivative of PBD, XIa or XIb. The reaction of carboxylic acid II with 4-(omega-aminoacetyl)biphenyl in the presence of CDI gives N-acyl-alpha-aminoketone VII; the analogous compound VI has been prepared by acylating omega-aminoacetophenone with acyl chloride III. The cyclization of these compounds gives bifluorophores Xa - Xd.

The low temperature phosphorescence spectra, polarization and the lifetime of the phosphorescence for five derivatives of 2-(biphenyl-4′-yl)-5-phenyl-1,3,4-oxadiazole (PBD) were measured. Two chemical pathways were found to force molecules of the PBD-type to phosphoresce: introducing a substituent with a localized low-energy nπ* state or substitution by a heavy atom (bromine). In both cases, the emitting, i.e. the lowest excited triplet state, is of the ππ* character. The T1 characteristics of the non-phosphorescent PBD were estimated by analogy. The vibrational structure of the phosphorescence spectral bands yields the information on the planarity of PBD-type chromophore in the excited T1 state.

The room and low temperature absorption and fluorescence spectra and the fluorescence quantum yields and lifetimes of ten derivatives of 2-(biphenyl-4′-yl)-5-phenyl-1,3,4-oxadiazole with a substituent in the para-biphenylyl position are reported. The theoretical spectral characteristics of the electronic transitions of the derivatives with strong electro-releasing (-NH2) and strong electron-withdrawing (-NO2) substituents have been calculated by the PPP method. Differences between the spectral characteristics of the phenyl- and biphenyl-substituted PBDs are explained on the basis of the charge transfer character of the first electronic transition. No fluorescence has been observed for the carbonyl, thiocarbonylamide and nitro derivatives. An efficient non-radiative deactivation mechanism involving low energy nπ* states localized on the substituent is assumed for these cases. The planarity of the compounds under study both in their ground and the lowest excited singlet ππ* state is discussed on the basis of the vibrational structure of the absorption and fluorescence spectra and on the basis of quantum chemical calculations.

The reaction of acetylacetone or sodium salt of oxymethyleneacetone with corresponding aldehydes has been used to prepare 3,5-diacetyl-1,4-dihydropyridines III which have been oxidized to diacetylpyridines VII. These compounds have been transformed by an acid-catalyzed reaction with benzaldehyde into the chalcones VIII which have been utilized for the Kröhnke synthesis of luminophoric terpyridines I and II.

The reaction of 2-cinnamoylfluorene II with quaternary pyridinium salts IIIa, IIIb in the presence of ammonium acetate, gave 2-fluorenyl-2,6-diarylpyridines IV. The complete assignment of 1H and 13C resonances by 2D NMR methods is given.

2-(4'-Acetylbiphenyl-4-yl)-5-phenyl-1,3,4-oxadiazole (I) was converted into α,β-unsaturated ketone II and pyridinium salt IV, which were used in preparation of triarylpyridines XIII-XIX by Kröhnke's method. Also the diketones V-VIII were obtained from derivative I and served as precursors for the synthesis of pyrazoles IX-XII. The discussion of 1H NMR spectra and luminescent properties of prepared bifluorophoric heterocyclic systems is given.

PBD was converted into 4’-substituted derivatives I-XII using usual electrophilic reagents. The decomposition of PBD, 4’-acetyl derivative I and 4’-nitro derivative VI with hydroiodic acid gave 4’-substituted 4-biphenylcarboxylic acids XIIIa-XIIIc and benzoic acid, respectively. The regioselectivity of the reaction was also proved by means of high resolution NMR spectroscopy.

The title carboxylic acid II prepared by hypobromide oxidation of 4'-acetyl derivative I was converted into its functional derivatives III-IX by standard preparative procedures. The C-acylation of 1,1-dichloroethene with acyl chloride III gave dichloroethenyl ketone X affording 2,4-disubstituted 1,3-thiazine-6-thiones XIa-XIe and XII by cyclocondensations with appropriate thioamides. The reactivity of heterocycles XIb, XIc was checked by their conversion into the expected products XIII-XV. IR and NMR spectroscopic patterns of the new prepared compounds are discussed.

The crystal and molecular structure of 1,2,4,4,6-pentamethyl-1,4-dihydropyridine-3,5-dicarbonitrile was solved by direct methods and anisotropically refined by the full-matrix least-squares method to a final R value 0.045 for 1 280 observed reflections (I > 3σ(I)). The compound crystallizes in the Pbca space group with lattice parameters of a = 12.021(1), b = 14.271(2), c = 13.465(1) Å, Z = 8. The six-membered 1,4-dihydropyridine ring of the title compound assumes the boat conformation, while the 1,4-dihydropyridine ring in the related compound, 1-ethyl-2,4,4,6-tetramethyl-1,4-dihydropyridine-3,5-dicarbonitrile, has the envelope conformation. The difference in the fluorescence intensities of these substances can be explained on the basis of this conformational difference. No intermolecular hydrogen bonds were found in the structure, indicating that the crystal is held together by van der Waals interactions.

Cyclocondensation of α,β-unsaturated aromatic ketones V and VIII with quaternary pyridinium salts VI in the presence of ammonium acetate gave 2,4,6-triarylpyridines I, aryl-substituted diaza-p-terphenyls IIa,b, diaza-p-quaterphenyls IIc,d and diaza-p-quinquephenyls IIe,f. All the new polyphenylene compounds exhibit characteristic luminiscence in the visible spectral region.

2,6-Dichloro-3,5-diformyl-4,4-dimethyl-1,4-dihydropyridines IIb-IId have been prepared by the Vilsmeier-Haack reaction of glutarimides I, and possible chemical transformations of the trimethyl derivative IIc have been examined. The bis-oxime IVa and bis-(2,4-dinitrophenylhydrazone) Vb are formed by the respective reactions of the formyl groups. The nucleophilic substitutions of chlorine give the corresponding derivatives IX-XII. The cyclocondensation reaction of compound IIc with the respective reagents gives the condensed heterocyclic derivatives VI, XIII, and XIV. The physico-chemical characteristics of the II-XIV compounds prepared are described.

Nitration of polyalkyated 3,5-dicyano-1,4-dihydropyridines Ia - Id to the first and second degrees has been studied leading to compounds II and III , and conversion of nitromethyl groups of these compounds into nitrile groups with formation of tricyano derivatives IV and tetracyano derivatives V has been followed. Also given is the fragmentation of the synthesized compounds II-V by an electron impact in mass spectrometer and further spectral characteristics.

Reaction of the title compound I with nitric acid in acetic afforded a mixture of products which on column chromatography afforded 5-cyano-4,4,6-trimethyl-2-nitromethylene-3-oxo-1,2,3,4-tetrahydropyridine ( II ), ( Z )-5-(1-acetoxy-2-nitrovinyl)-3,5-dicyano-4,4-dimethyl-2-pyrazoline ( III ) and 3-acetoxy-3-cyano-4,4,6-trimethyl-5-oxo-2,3,4,5-tetrahydropyridazine ( IV ). Reaction of I with nitrating mixture in chloroform gave only the compound II . The probable mechanism of formation of compounds II, III and IV , together with their 1 H NMR, 13 C NMR, IR and mass spectra, is discussed.

Electronic absorption spectra of 1,4-dihydropyridines I-XII have been interpreted by means of the SCF-PPP method. Possibility of interpretation of the said spectra of 4-substituted derivatives V-XII as superposition of two independent chromophoric systems is discussed.

Chemical transformations have been studied of nitromethyl group in 3,5-dicyano-1,4,4,6-tetramethyl-2-nitromethyl-1,4-dihydropyridine (I) brought about by action of acetic acid and/or acetic anhydride, diazomethane, and phosphorus trichloride and giving also the products VIII and IX of intramolecular reaction with the neighbouring cyano group. Spectral characteristics of the synthetized compounds and their splitting by electron impact in mass spectrometer are given, and mechanism of the individual transformations is discussed.

A series of 29 substituted 1,4-dihydropyridines has been studied in acetonitrile by means of voltammetric methods at a platinum electrode. The formation of radical intermediates has been investigated with the help of ESR spectroscopy. A cell for in situ electrochemical generation of radical ions in ESR measurements has been described. In the detection of radicals a comparison has been made between fast cyclic voltammetry (up to 50 V s−1) at low temperatures (down to −40°C) and ESR spectroscopy.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDevelopment in dihydropyridine chemistryJosef Kuthan and A. KurfurstCite this: Ind. Eng. Chem. Prod. Res. Dev. 1982, 21, 2, 191–261Publication Date (Print):June 1, 1982Publication History Published online1 May 2002Published inissue 1 June 1982https://pubs.acs.org/doi/10.1021/i300006a012https://doi.org/10.1021/i300006a012research-articleACS PublicationsRequest reuse permissionsArticle Views894Altmetric-Citations93LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts