Synthetic studies on mesoionic compounds. The mesoionic 1,3-diazol-4-one system

The synthesis of the mesoionic 1,3-diazol-4-one system is discussed. The intermediate to this system and the attempted cyclizations are described in detail. Further comments on the stability of these mesoionic compounds are also made.     

Mesoionic purinone analogs. II. A PPP π-SCF variable integral study of mesoionie analogs based upon six-membered ring mesoionie systems

A large virtually unknown class of mesoionic structures which are isoconjugate to the purinones may be formulated as bicyclie derivatives of known six-membered ring mesoionie compounds. These mesoionic purinone analogs have been investigated via variable-electronegativity PPP-SCF treatments of their π-electron systems. The electronic structures of these analogs are compared with those of their covalent isomers and with other mesoionie purinone analogs.     

Mesoionic purinone analogs. III. The synthesis and properties of mesoionic thiazolo[3,2-a ] pyrimidine-5,7-diones

A number of mesoionic thiazolo[3,2-a ]pyrimidine-5,7-diones, isoconjugate mesoionic analogs of xanthinc, were prepared by the condensation of 2-alkylaminothiazoles with bis(2,4,6-trichloro-phenyl)malonate esters. The ground state molecular properties and reactions of these compounds were found to be consistent with predictions based upon previous SCF molecular orbital treatments of the π-systems of these analogs.     

A facile preparation of some novel class II mesoionic xanthine acyclonucleosides

The synthesis of the first examples of Class II mesoionic xanthine acyclonucleosides is described. A series of mesoionic anhydro-(8-methoxyalkyl-5-hydroxy-7-oxothiazolo[3,2-a]pyrimidinium hydroxides), Class II mesoionic analogs isoconjugate with xanthine, were prepared by the thermal condensation of methoxyalkyl-2-aminothiazoles with substituted bis(2,4,6-trichlorophenyl)malonic esters. The memoxyalkyl-2-aminothiazoles were prepared via an aromatic nucleophilic substitution reaction between 2-bromothiazole and the appropriate methoxyalkylamine in excess. The resulting 8-methoxyalkyl-substituted mesoionic xanthines were demethylated using iodotrimethylsilane in acetonitrile at room temperature to afford the corresponding mesoionic anhydro-(8-hydroxyalkyl-5-hydroxy-7-oxothiazolo[3,2-a]pyrimidinium hydroxides) as the Class II mesoionic xanthine acyclonucleosides.     

Mesoionic purinone analogs. VIII. Synthesis and properties of mesoionic 5-substituted-6-methylimidazo[1,2-c]pyrimidine-2,7-diones

Mesoionic imidazo[1,2-c]-pyrimidine-2,7-diones 1a-c , analogs of purine-2,8-dione, were prepared from 4-amino-l-methylpyrimidin-6-ones 6a-c . These mesoionic purinone analogs were found to exist predominantly in the C3-H tautomeric form 1 and to undergo hydrolytic ring-opening reactions to produce 2-(4-imidazol-idon-2-ylidenyl)acetamides. Reaction of 1c with dimethyl acetylene dicarboxylate produced triazacyclopent-[cd]indene 25 via 1,3-dipolar cycloaddition.     

A facile and ecofriendly functionalization of multiwalled carbon nanotubes by an old mesoionic compound

This work reports for the first time a straightforward solvent-free chemical procedure to gain access to Δ-1-pyrroline grafted onto multiwalled carbon nanotubes by the 1,3-dipolar cycloaddition of the mesoionic 4-methyl-2-phenyloxazol-5(4H)-one.     

Adamantylazoles: XI. Reaction of 1-phenyltetrazole-5-thione with adamantan-1-ol in strong acids

The reaction of 1-phenyltetrazole-5-thione with adamantan-1-ol in sulfuric acid gave 3-(1-adamantyl)-1-phenyltetrazole-5-thione having a mesoionic structure, 5-(1-adamantylsulfanyl)-1-phenyltetrazole, and 3-(1-adamantyl)-5-(1-adamantylsulfanyl)-1-phenyltetrazolium hydrogen sulfate. Hydrolysis of 5-(1-adamantylsulfanyl)-1-phenyltetrazole led to the formation of 1-phenyltetrazol-5-one. The adamantylation process is reversible.     

Annelation of α,β-unsaturated esters to thian-3-one 1-oxides using dianion of ω-(methylsulfinyl)acetophenone

β-Monosubstituted α,β-unsaturated esters undergo an annelation with dilithio salt of ω-(methylsulfinyl)-acetophenone to produce 5-substituted 6-benzoylthian-3-one 1-oxides.     

Synthesis of 2H-pyrano[2,3-b]quinolines. Part I

3,4-Dihydro-2H-pyrano[2,3-b]quinolines 5a-e and 2H-pyrano[2,3- b ]quinolines 10a-c were synthesised starting from the appropriate ω-chloro-n-valeroylanilides 2a-e . Compounds 10a-c were transformed to analogs of the novel antihypertensive agent Cromakalim ( 1 ).     

Synthesis of peptides containing 1,2,3,4-tetrahydroquinoline-2-carboxylic acid. Part 3. Cyclization of dipeptides and amides with acetic anhydride

Treatment of protected dipeptides containing 1,2,3,4-tetrahydroquinoline-2-carboxylic acid with acetic anhydride affords only 1H,3H,5H-oxazolo[3,4-a]quinolin-3-one derivatives. The formation of a-acylaminomethylketones, arising from the competitive Dakin-West reaction, was generally observed when the cyclization procedure was extended to some amides of the cyclic imino acid. The preferential stabilization of one of two probable mesoionic intermediates seems to determine the preferred pathway.     

Modified coumarins. 14. Synthesis of 7-hydroxy-[4,3′]dichromenyl-2,2′-dione derivatives

New derivatives of 3-(2-oxochromen-4-yl)chromen-2-one, modified analogs of natural dicoumarins, were prepared from substituted coumarin-4-acetic acids.Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 358–365, September–October, 2004.     

Stereoselectivity of an ω-transaminase-mediated amination of 1,3-dihydroxy-1-phenylpropane-2-one

The stereoselectivity of a recently isolated ω-transaminase from Chromobacterium violaceum in the amination of 1,3-dihydroxy-1-phenylpropan-2-one has been determined. The enzyme is not enantioselective towards a racemic mixture of 1,3-dihydroxy-1-phenylpropan-2-one but is highly stereoselective forming (2S)-2-amino-1-phenyl-1,3-propanediols in >99% ee.     

Concise synthesis of ω-fluoroalkylated ketoesters. A building block for the synthesis of six-, seven-, and eight-membered fluoroalkyl substituted 1,2-diaza-3-one heterocycles

A concise and general synthetic route toward the small and medium-sized fluoroalkyl substituted 1,2-diaza-3-one heterocyclic ring skeletons via a sequential reaction of condensation and ring-closure reaction of ω-fluoroalkylated ketoesters 4 with hydrazines 5 catalyzed by 10-20 mol % TsOH has been developed. A practical preparation of biologically interested ω-fluoroalkylated ketoesters 4, which were subsequently subjected as a fluorine-containing building block to the synthesis of 1,2-diaza-3-one heterocycles has been optimized. Trifluoromethyl substituted seven- and eight-membered 1,2-diazapinone 8, 1,2-diazocinone 10 were also obtained via this sequential reaction of δ- (or ?-) trifluoromethyl ketoesters with hydrazine hydrates in acidic condition. In contrast, the sequential reaction of ω-fluoroalkylated δ- or ?-ketoesters with aryl hydrazines under the same conditions did not result in the formation of diazepinones and diazocinones, and instead, the reaction provided a direct access to the biologically important 2-fluoroalkyl-indole-3-carboxylate derivatives via a Fisher indole synthesis.     

Quantum-Chemical Study of the Structure and Reactivity of Pyrazol-5-ones and Their Thio and Seleno Analogs: VI. Tautomeric and Acid-Base Properties of 3-Methyl-1-phenyl-4,5-dihydropyrazol-5-one, 3-Methyl- 1-phenyl-4,5-dihydropyrazole-5-thione,and 3-Methyl-1-phenyl-4,5-dihydropyrazole-5-selenone

The relative stabilities of tautomeric forms of 3-methyl-1-phenylpyrazol-5-one and its 5-thioxo and 5-selenoxo analogs, as well as their acid-base properties in the gas phase, were estimated in terms of nonempirical calculations and density functional theory. According to the results of both calculation methods, the CH tautomer of 3-methyl-1-phenylpyrazol-5-one is the most stable. The stabilities of the XH and CH forms of its heteroanalogs (X = S, Se) are comparable; the relative stability of the SeH (SH) tautomers increases when thermal corrections, zero-point energy, and electron correlation effects are taken into account. The two methods indicate increase in the gas-phase acidity of the title compounds on variation of the heteroatom in the series O 相似文献   

Ring transformation of pyrimidines to pyridines. Synthesis of 4-alkylaminopyridin-2-ones by alkaline hydrolysis of 6-(2-dimethylaminovinyl)uracils

Alkaline hydrolysis of 1,3-disubstituted 6-(2-dimethylaminovinyl)uracils 2 induced a novel ring transformation giving 4-alkylaminopyridin-2-ones 3 via ring-opening and ring-closure processes. The 4-methylamino-3-nitropyridin-2-one ( 3a ) thus obtained was employed for the synthesis of 3-deazahypoxanthine derivative 8. 4-Alkylamino-3-cyanopyridin-2-ones 11 , ricinine analogs, were also prepared by the reaction of 4-chloro-3-cyano-1-methylpyridin-2-one ( 10 ) with amines.     

Condensed heterocycles with a thiazole nucleus. 8. Thiazolo[4,3-a]pyrimido[5,4-e]pyrimidines

Condensation of 4-amino-2-methylthiothiazolium salts with 2,4,6-trichloro-5-formylpyrimidine or 3-R-2,4-dioxo-6-chloro-5-formyl-1,2,3,4-tetrahydropyrimidines yielded mesoionic derivatives of a new heterocyclic system — thiazolo[3,4-a]pyrimido[5,4-e]-pyrimidine — which can be used for the synthesis of polymethine dyes. The absorption maxima of these dyes are bathochromically shifted by 10–20 nm relative to the maxima of the thiazolopyrimidine analogs. The structure of the compounds synthesized was demonstrated by the PMR and IR spectra.For communication 7, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1126–1128, August, 1984.     

An ab initio study of the valence tautomerism of type B mesoionic rings

The MP2 calculated Gibbs free energies of a series of type B mesoionic rings and their acyclic valence tautomers suggest that in the gas phase the relative stability of the mesoionic ring increases with single bond strength (SS > RNNR > OO). Inclusion of aqueous solvation in the calculations further favours the stability of the mesoionic ring by ～10–15 kcal mol^?1. Replacement of CR groups at ring positions by nitrogen atoms results in a significant increase in the relative stability of the mesoionic ring. Calculations of aromatic stabilization energy (ASE), together with the Bird aromaticity index (I₅), suggest that aromaticity decreases with aza substitution and the increase in relative stability is attributable to charge stabilisation by the electronegative nitrogen atoms, which more than compensates for any loss of aromaticity.     

Formation of acetamido-Aza-steroids

Beckmann rearrangement of 3α- and 3β-acetamido-5α-androstan-17-one oximes gives homo-aza compounds and the corresponding “second order” Beckmann cleavage ω-cyanoolefin. The mixture of the compounds produced, was separated by column chromatography. The structure of the lactams and the exocyclic nitriles was apparent from ir and nmr spectra.     

Mass spectrometry of modified nucleic acid bases and nucleosides. 2. Class II mesoionic nucleosides and bases derived from thiazolo[3,2-a]pyrimidine-5,7-diones

The mass spectral characteristics of novel Class II mesoionic heterocyclic bases and nucleosides based on the thiazolo[3,2-a]pyrimidine-5,7-dione system have been examined using low and high resolution mass spectrometry and metastable ion analysis. The mass spectra of these Class II mesoionic nucleosides differ significantly from the spectra of “normal” nucleosides by the absence of fragment ions associated with the base plus portions of the sugar. The difference in fragmentation is rationalized on the basis of exclusive localization of the radical-charge site in the aglycone, a result of the mesoionic structure of these molecules. The fast atom bombardment (FAB) mass spectra of a Class I mesoionic nucleoside, 7-methylguanosine, is compared to the FAB mass spectra of the Class II mesoionic nucleosides.     

σ-Complexes in the Pyrimidine Series. 14. Dihydropyrimidine Analogs of Acyclonucleosides. Synthesis of 2,3-Dihydroxypropyl Derivatives of 4-Aryl-6-methyl-5-nitro-1,4(3,4)-dihydropyrimidin-2-ones

Methods have been developed for the synthesis of 5-nitro-1,4- and 5-nitro-3,4-dihydropyrimidin-2-one analogs of acyclonucleosides containing a 2,3-dihydroxypropyl fragment in positions 1 and 3 respectively of the dihydropyrimidine ring.