Studies on cycloimmonium ylids. Synthesis of some new 2,4,6-triaryl-substituted pyridines via pyridinium,picolinium and isoquinolinium ylids

Reaction of pyridinium phenacylids and their picolinium and isoquinolinium counterparts with substituted benzylideneacetophenones gave a wide variety of 2,4,6-triaryl-substituted pyridines which are expected to have some potential biological activities. Ammonium acetate in glacial acetic acid was used as the cyclization agent. The structures of resulting pyridines are supported by nmr and ir spectral data.     

Regio- and stereodirectivity in the reactions of isoquinolinium ylides with unsaturated nitriles

Reactions of isoquinolinium ylides with arylmethylenemalonitriles involve 1,3-dipolar cycloaddition, with the highly regio- and stereoselective formation of 2-aryl-3-benzoyl(or carbamoyl)1,1-dicyano-2,3-trans-1,2,3,10b-tetrahydropyrrolo[2, 1-a]isoquinolines. In contrast, N-phenacylisoquinolinium ylide reacts with aryl-methylenecyanothioacetamides differently, proceeding regio- and stereoselectively to give 4-aryl-2-hydroxy-3-(1-isoquinolinio)-2-phenyl-3-cyano-3,4-trans-1,2,3,4-tetrahydropyridine-6-thiolates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2593–2599, November, 1990.     

Regio- and stereoselective synthesis of tetrahydroindolysines,tetrahydropyridin-6-olates,and cyclopropanes from pyridinium ylides and unsaturated nitriles

The regio- and stereoselectivity of the reactions of pyridinium ylides with unsaturated nitriles are dependent on the electronic nature of the substituent in position 3 of the pyridine ring. The reaction of 1-carbamoylmethylide-3-cyanopyridinium with arylmethylenemalononitriles or arylmethylcyanoacetic esters proceeds regio- and stereoselectively with the formation of substituted 2-aryl-3-carbamoyl-6-cyano-2,3-trans- or 2,3-cis-1,2,3,8a-tetrahydroindolysines. The condensation of pyridinium 1-carbamoylmethylide with arylmethylenecyanoacetic ether leads to 4-aryl-2-oxo-3-(1-pyridinio)-5-cyano-3,4-trans-1,2,3,4-tetrahydropyridin-6-olates. The reaction of pyridinium (3-methylpyridinium) 1-carbamoylmethylide with arylmethylenemalononitriles results in the formation of 2-aryl-1,1-dicyano-3-carbamoyl-3-(1-pyridinio)- or (3-methyl-1-pyridinio)-1-propanides, which undergo stereoselective 1,3-transelimination with the formation of 3-aryl-1,1-dicyano-2-carbamoylcyclopropanes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 146–155. January, 1991.     

Regio- and stereoselectivity in the addition reactions of CH-acids to aldehydes under the conditions of phase-transfer catalysis

The regio- and stereoselectivity of the reactions of carbanions, generated from alkanals, carboxylates of the type XYCHCOOEt (X = EtOOC, CN, Ac; Y = H, Br), or derivatives of 3-methyl-4-phosphono-2-butenoic acid using PTC techniques, with aldehydes of various types (alkanals, ,-enals, cross-conjugated enedials, benzaldehydes,etc.) are reviewed. The factors affecting the outcome of these reactions are discussed. The carbanion analogs, triphenylphosphorus ylides, are shown to attack selectively at one of the aldehyde groups of aromatic dialdehydes. The regularities found for the title reactions were used in the syntheses of some biologically active isoprenoids.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1867–1885, October, 1995.     

Basicities and transformations of pyrylium and pyridinium salts containing p-aminophenyl substituents

On the basis of the measured basicity constants of pyrylium and pyridinium salts containing p-aminophenyl substituents it is shown that the positive charge in the pyrylium cation is considerably higher than in the pyridinium cation. The constants of the pyrylium and pyridinium substituents, which show that the magnitude of the electronic effect of the pyrylium ring is considerably higher than that of the pyrydinium ring, were calculated. The reaction of the indicated pyrylium salts with some electrophilic and nucleophilic reagents was examined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1025–1028, August, 1976.     

Regioselectivity of the reactions of pyridinium and quinolinium salts with various nucleophiles (Review)

The factors determining the regioselectivily of nucleophilic addition to pyridinium and quinolinium cations are examined. Published data of the last IS years are summarized.N. D. Zelinski Institute of Organic Chemistry, Russian Academy of Sciences, Moscow. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 774–815, June, 1995. Original article submitted April 25, 1995.     

Alkylamino group exchange upon recyclization of pyridinium salts into anilines

Nitropyridiniium salts react with primary or secondary amines to form alkyl or dialkylanilines as result of recyclization of pyridine nuclei. The alkylamine or dialkylamine group is included in the reaction final product at the open form stage. Aqueous methylamine may open even non-quatèrnized nitropyridines with the following ring closure to alkylanilines.     

Photocyclization reactions of cyclohexa- and cyclopenta-fused pyridinium salts. Factors governing regioselectivity

The results of studies described in this report show that irradiation of 1,2-cyclopenta-fused pyridinium perchlorate in aqueous base promotes a remarkably regioselective photocyclization reaction that results in exclusive formation of a single tricyclic allylic alcohol. Moreover, transformation of this photoproduct to a spirocyclic amido diester followed by enzymatic desymmetrization produces an enantiomerically pure monoalcohol. This chemistry comprises a highly concise sequence for the preparation of what should become a useful synthon in synthetic organic chemistry.     

Synthesis of indolizines and pyridinium ylids from 4,5-disubstituted α-picolines

New 1,3-diacetylindolizines were obtained from 4-phenyl- and 4-benzyl-2,5-dimethylpyridines; some transformations involving their acetyl groups were realized. The same pyridine bases were used in syntheses of pyridinium ylids. The transformations of the latter to indolizines were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 506–510, April, 1976.     

Platinum-promoted cyclization reactions of amino olefins : II. Regio- and stereoselectivity in the cyclization reactions of C-methyl substituted pent-4-enylamines

The compounds 1-, 2- and 3-methylpent-4 enylamine cyclize, in a reaction medium containing [PtCl₄]^2-, to the corresponding cis- and trans-dimethylpyrrolidines showing marked regio and stereoselectivity effects. The following cyclization reactions are also reported: a) that of hex-4-enylamine which gives a mixture of 2-ethylpyrrolidine and 2-methylpiperidine, b) that of 2,2-dimethylpent-4-enylamine which produces 2,4,4-trimethylpyrrolidine and c) that of 2,2-dimethylhex-4-enylamine which results in the formation of 2-ethyl-4,4-dimethylpyrrolidine and 2-methyl-5,5-dimethylpiperidine.The X-ray crystal structures of trans-[PtCl₂(amine)(Et₃P)] (amine = cis-2, 4-dimethylpyrrolidine and cis-2,3-dimethylpyrrolidine) are reported.     

The reaction of N-nitrosamines with pyridinium salts

N-Nitrosamines react readily with pyridinium salts containing an activated methylene group to give hydrazones. This reaction may serve as the basis for the routine determination of N-nitrosamines.     

Reactivity of pseudobases from pyridinium salts competition between hydrogen transfer and ring-opening reactions

The reactions of 3-cyano-1-methylpyridinium iodide (1a) and l-benzyl-3-cyanopyridinium chloride (1b) in aqueous NaOH have been studied over a range of concentrations from N 0.5 to N 2.5 with respect to the hydroxide ion, and with the concentrations of the reactants at different ratios. It has been found that the intermediate, not isolable pseudobases can undergo, depending on the experimental conditions, two competitive reaction channels, namely, a redox process leading to the dihydropyridines 3–5 and pyridones 2,6, and a ring-opening reaction leading to the pentadienenitrile 7, 2-imino-3-pyridinecarbaldehyde 8, and 2-(aryl)alkylamino-3-pyridinecarbaldehyde 9.     

Regio- and stereoselectivity of cycloadditions of C-(Trifluoromethyl)nitrone with olefins

N-Methyl-C-(trifluoromethyl)nitrone ( 1 ) cycloadds with various olefins to give 2-methyl-3-trifluoromethyl-isoxazolidines. Predominant formation of 5-substituted isoxazolidines in the cycloadditions with monosubstituted olefins is observed and this high regioselectivity is attributed to the dipole-LUMO controlled interaction, being rationalized on the basis of molecular orbital calculation of 1 . ‘Anti’-favorable approach of 1 to olefin in the transition state is considered from the configuration of the cycloadducts, pointing out the very weak secondary orbital interaction between trifluoromethyl group and olefin-substituents including phenyl or ester group.     

Cation-pi interactions of a thiocarbonyl group and a carbonyl group with a pyridinium nucleus

Attractive interactions between a thiocarbonyl group and a pyridinium nucleus, and between a carbonyl group and a pyridinium nucleus have been proven by (1)H and (13)C NMR studies, UV-vis spectral analyses, and X-ray crystallographic analyses of nicotinic amides 1 and 3, and pyridinium salts 2 and 4. Comparison of the Deltadelta values, which are the differences in the chemical shifts with reference compounds 5 or 6, showed that the absolute Deltadelta values of 2 and 4 are much larger than those of 1 and 3. In the UV-vis spectra, the n-->pi absorption of the C=S group of 2a exhibited a significant blue shift in CHCl(3). X-ray crystallographic analysis of 1-4 clearly showed that the C=S group of 2a and the C=O group of 4 are very close to the pyridinium moiety compared to the case of 1 and 3. In addition, the X-ray crystal packing structure of 2a showed the C=S group is sandwiched between two pyridinium rings. These experimental results strongly suggested the existence of attractive (C=S)...Py(+) and (C=O)...Py(+) interactions in solution and in crystal. The optimized geometries of 1 and 2 calculated at the HF/6-311G level are in good agreement with their X-ray geometries. MP2/6-311G calculations for the model systems of pyridinium salts 2 and 4 predicted that the electrostatic and induction energies are the major source of the attractive interactions. Since the larger contribution of electrostatic and induction interactions are characteristic features of cation-pi interactions, the (C=S)...Py(+) and (C=O)...Py(+) interactions would be classified as a cation-pi interaction.