New routes to the v-triazolo[1,5-a]pyridine and pyrazolo[1,5-a]pyridine ring systems

New routes to the v-triazolo[1,5-a]pyridine and pyrazolo[1,5-a]pyridine ring systems are described. Treatment of the N-amine salts of 2-picolinealdehyde oxime or 2-pyridyl ketone oximes with polyphosphoric acid gave v-triazolo[1,5-a]pyridines in fair yields. Treatment of 2-picolyl ketones or their oximes with O-mesitylenesulfonylhydroxylamine produced directly pyrazolo-[1,5-a]pyridines. These reactions were extended to the quinoline cases.     

Anomalous Beckmann Reaction of 4-Aryl-2,7,7-trimethyl-5-oxo-5,6,7,8-tetrahydroquinoline Oximes in Polyphosphoric Acid. 1. New Synthesis of 1-Ethoxycarbonyl-2,5,5-trimethyl-5,6-dihydro-4H-pyrido[2,3,4-k,l]acridines

Transformations of oximes of 4-aryl-2,7,7-trimethyl-5-oxo-5,6,7,8-tetrahydroquinolines in PPA have been studied. It is shown that the reaction, depending on substituent at position 4 of quinoline ring, can occur in three directions: aromatization of the saturated ring (Semmler-Wolff aromatization), formation of azepinones - normal products of Beckmann rearrangement, and formation of pyridoacridines.     

2-苄基-1,3-二氢-4-异喹啉酮及其衍生物的合成

本文合成了2-苄基-1,3-二氢-4-异喹啉酮的四种3-位亚甲基取代衍生物，四种氧酰基肟和两种6-苄基-5H-异喹啉并[4,3-b]喹啉衍生物。新化合物的结构经元素分析、红外光谱、核磁共振谱证实。     

Microwave-assisted syntheses of N-heterocycles using alkenone-, alkynone- and aryl-carbonyl O-phenyl oximes: formal synthesis of neocryptolepine

This research aimed to provide a new and "clean" synthetic method that would enable both known and novel N-heterocycles to be prepared efficiently. O-Phenyl oximes were found to be excellent precursors for iminyl radicals with a variety of acceptor side chains. Dihyropyrroles were made in good yields from O-phenyl oximes containing pent-4-ene acceptors. The analogous process with a hex-5-enyl acceptor did not yield a dihydropyridine, probably because the 6-exo-trig ring closure of the iminyl radical was too slow to compete with H-atom abstraction. The iminyl radical from a precursor with a pent-4-yne type side chain underwent ring closure followed by rearrangement to afford a pyrrole derivative. Suitably substituted iminyl radicals ring closed readily onto aromatic acceptors, thus enabling several polycyclic systems to be accessed. Quinolines were made from 3-phenylpropanones via their O-phenyl oximes. Syntheses of phenanthridines starting from 2-formylbiphenyls were particularly efficient, and this approach enabled the natural product trisphaeridine to be made. Starting from 2-phenylnicotinaldehyde derivatives, ring closures of the derived iminyl radicals onto the phenyl rings yielded benzo[h][1,6]naphthyridines. Similarly, ring closure onto a phenyl ring from a benzothiophene-based iminyl yielded a benzo[b]thieno[2,3-c]quinoline. By way of contrast, iminyl radical ring closure onto pyridine rings was not observed. However, iminyl radicals did cyclize onto indoles, enabling indolopyridines to be prepared. The latter route was exploited in a short formal synthesis of neocryptolepine starting from 2-((1H-indol-3-yl)methyl)cyclohexanone.     

Pyrrole Oximes: Synthesis, Reactions, and Biological Activity. (Review)

Data on the production methods and reactions of pyrrole aldoximes and ketoximes and their derivatives are reviewed. The synthesis of new heterocycles from the pyrrole oximes is examined separately. The principal results from investigation of the biological activity of pyrrole oximes are described.     

Indole and Isatin Oximes: Synthesis, Reactions, and Biological Activity. (Review)

Data on methods for the production of isatin and indole aldoximes, ketoximes, and amidoximes and their reactions are reviewed. Individual syntheses of new heterocycles from indole and isatin oximes are discussed. The principal results from investigation of the biological activity of derivatives of the oximes are also presented.     

Furan and Thiophene Oximes: Synthesis, Reactions, and Biological Activity. (Review)

Data on methods for the production of furan and thiophene aldoximes, ketoximes, and amidoximes and their reactions are reviewed. The synthesis of new heterocycles from furan and thiophene oximes and the biological activity of derivatives of the oximes are discussed individually.     

Pyridine Oximes: Synthesis, Reactions, and Biological Activity. (Review)

Data on methods for the production of pyridine aldoximes, ketoximes, amidoximes, and their derivatives and their reactions are reviewed. The synthesis of new heterocycles from pyridine oximes is discussed separately. The principal results of research into the biological activity of the oximes are presented.     

Oximes of five-membered heterocyclic compounds with three and four heteroatoms 2. Synthesis of derivatives,reactions, and biological activity (Review)

Data on the reactions of triazole, tetrazole, dioxazole, oxadiazole, and thiadiazole aldoximes, ketoximes, and amidoximes, their synthesis, and the reactions of their derivatives are reviewed. The synthesis of new heterocycles based on the oximes of five-membered heterocyclic compounds with three and four heteroatoms is examined separately. The principal results from investigation of the biological activity of ethers of these oximes are also presented. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 963–990, July, 2008.     

Electroreduction of aromatic oximes: diprotonation, adsorption, imine formation, and substituent effects

Aromatic oximes are reduced in aqueous solution in a four-electron process. The reducible species in the pH range 5-8 is a diprotonated form of the oxime. This species is generated in the course of electrolysis in the vicinity of the electrode surface from the adsorbed neutral form of the oxime. The reduction is initiated by a cleavage of the N-O bond. The diprotonation facilitates the reduction process by the preformation of OH2+ as a good leaving group and by a positive charge on the azomethine nitrogen. Diprotonation has been proven based on shapes of i = f(pH) plots, by observed shifts of half-wave potentials with pH and by comparison with the reduction of nitrones. Some observed deviations from theoretical i = f(pH) plots were attributed to the role of adsorption on the rate of protonation. Adsorption is also responsible for dips on some of the i-E curves. Adsorption plays a role at concentrations as low as 1 x 10(-5) M, when the electrode surface is still not fully covered. This indicates that catalyzed protonation occurs on islets of adsorbed materials. At pH 2-5 the studied oximes in the vicinity of the electrode are predominately present in a protonated form, which is less strongly adsorbed. In this pH range the protonation takes place in a homogeneous reaction layer of the electrode. It yields a monoprotonated form, which is reduced. The separation of two two-electron waves observed for some oximes in acidic media serves as an experimental proof of the formation of imines as reduction intermediates. This separation is caused by the differences in pKa values of protonated forms of oximes and imines. The effects of substituents in the para position on the benzene ring are characterized by correlation with the Hammett substituent constant sigmax. This has been proven at pH 1.5 for substituted benzaldehyde oximes and at pH 5.0 for substituted acetophenone oximes.     

Photochemical radical cyclization of γ,δ-unsaturated ketone oximes to 3,4-dihydro-2H-pyrroles

3,4-Dihydro-2H-pyrroles are synthesized from γ, δ-unsaturated oximes by photochemical radical cyclization with 1,5-dimethoxynaphthalene (DMN) as the sensitizer. The cyclization of alkyl ketone O-acetyloximes proceeds via photosensitized electron transfer in the presence of acetic acid, while conjugated oximes of aryl and α,β-unsaturated ketones are cyclized via energy transfer.     

Oximes of five-membered heterocyclic compounds with two heteroatoms 2. Reactions and biological activity (Review)

Data on the reactions of oxazole, thiazole, pyrazole, and imidazole aldoximes, ketoximes, amidoximes, and their derivatives are reviewed. The synthesis of new heterocycles based on the oximes of five-membered heterocyclic compounds with two heteroatoms are considered separately. The principal results from investigation of the biological activity of the ethers of these oximes are also presented. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1123–1155, August, 2007.     

Studies in pyran,its analogs,and related compounds

The lithium aluminum hydride reduction of the ethers and tosylates of chroman-4-one oxime and related compounds has been studied. It has been found that the ethers of the oximes, like the oximes, do not undergo a normal, but rather an anomalous, reduction. The tosylates of the oximes exhibit a higher tendency to undergo anomalous reduction than the corresponding oximes. During the synthesis of the ethers of the oximes it was established that the use of dimethylformamide as the medium for alkylation of the oxime salts helps to suppress the side reaction forming nitrones.For part XXXVII, see [23].     

O-carbamoyl oximes as potential analgesics

Preparation of oxadiazinones 2 , from α-anilinoacetophenone oximes and O-carbamoyl-2,3-dihydro-4-quinolinone oximes 3 , from quinolinones are described.     

Competitive adsorption isotherm modelling of heterocyclic nitrogenous compounds,pyridine and quinoline,onto granular activated carbon and bagasse fly ash

In the present study, simultaneous adsorption of quinoline and pyridine onto adsorbents such as granular activated carbon (GAC) and bagasse fly ash (BFA) from pyridine–quinoline binary aqueous solution was studied at various temperatures (288–318 K). Gathered equilibrium adsorption data were further analysed using various multicomponent competitive isotherm models such as non-modified and modified competitive Langmuir isotherms, extended-Langmuir isotherm, extended-Freundlich model, Sheindorf–Rebuhn–Sheintuch (SRS) model, and non-modified and modified competitive Redlich–Peterson isotherm model. It was observed that increase in pyridine concentration decreased the total adsorption yield and the individual adsorption yield for both the quinoline and pyridine for both the adsorbents GAC and BFA at all the temperatures studied. Identical trend was observed during the equilibrium uptake of pyridine on to GAC and BFA with an increase in quinoline concentration. The extended-Freundlich model satisfactorily represented the binary adsorption equilibrium data of quinoline and pyridine onto GAC and BFA.     

An Efficient,Selective and Inexpensive Supported Oxidant for the Regeneration of Carbonyl Compounds from Oximes,Semicarbazones, 4-Phenylsemicarbazones,and P-Nitrophenylhydrazones

Dimethylammonium chlorochromate adsorbed on silica gel (DMCC/SiO₂) makes the regeneration of carbonyl compounds from oximes, semicarbazones, 4-phenyl-semicarbazones, and p-nitrophenylhydrazones in good yields under mild and non-aqueous conditions.     

Structure, stability, and interconversion barriers of the rotamers of cis-[Pt(II)Cl(2)(quinoline)2] and cis-[Pt(II)Cl(2)(3-bromoquinoline)(quinoline)] from X-ray crystallography, NMR spectroscopy and molecular mechanics evidence

Reported are the preparations of cis-[PtCl(2)(quinoline)(2)] and cis-[PtCl(2)(3-bromoquinoline)(quinoline)] and an investigation of the stabilities and interconversion of the rotamer forms of these complexes. Both head-to-head (HTH) and head-to-tail (HTT) rotamer forms are found in the crystal structure of cis-[PtCl(2)(quinoline)(2)]. The NOESY NMR spectrum of cis-[PtCl(2)(quinoline)(2)] in dmf-d(7) at 300 K is consistent with conformational exchange brought about by rotation about the Pt-N(quinoline) bonds. H.H nonbonded distances between H atoms of the two different quinoline ligands were determined from NOESY data, and these distances are in accord with those observed in the crystal structure and derived from molecular mechanics models. cis-[PtCl(2)(3-bromoquinoline)(quinoline)] was prepared to alleviate the symmetry-imposed absence of inter-ring H2/H2 and H8/H8 NOESY cross-peaks for cis-[PtCl(2)(quinoline)(2)]. Molecular mechanics calculations on the complexes show the HTT rotamers to be 1-2 kJ mol(-)(1) more stable than the HTH forms, consistent with the (1)H spectra where the intensities of resonances for the two forms are approximately equal. Variable-temperature (1)H NMR spectra of cis-[PtCl(2)(quinoline)(2)] in dmf-d(7) indicate a rotational energy barrier of 82 +/- 4 kJ mol(-)(1). Variable-temperature (1)H NMR spectra indicate that the Br substituent on the quinoline ring does not affect the energy barrier to interconversion between the HTT and HTH forms (79 +/- 5 kJ mol(-)(1)). The steric contribution to the rotation barrier was calculated using molecular mechanics calculations and was found to be approximately 40 kJ mol(-)(1), pointing to a possible need for an electronic component to be included in future models.     

Mass spectra of some syn- and anti-aromatic aldoximes

The mass spectra of eight pairs of geometric isomers of aromatic oximes and four other single aromatic oximes are reported. The loss of H₂O, HO and HCN are major fragmentations from the molecular ion of all the benzaldoximes studies; however, the loss of HCN from the molecular ion did not occur in the oximes of 9-phenanthraldehyde, 1-naphthaldehyde and 2-naphthaldehyde. The halogen substituted benzaldoximes eliminate HCNO and H₂CNO forming an additional fragmentation pathway from the molecular ion. In general, variations were found for each pair of syn- and anti-oximes but no consistent patterns could be found in the spectra for all the syn-isomers versus all of the anti-isomers. The geometric isomerism of four oximes previously reported in the literature have been established for the first time as anti-m-bromobenzaldoxime, syn-9-phenanthraldoxime, syn-1-naphthaldoxime and syn-2-naphthaldoxime. Three new oxime acetates were prepared and their mass spectra are discussed.     

Chemistry of N,N‐Bis(silyloxy)enamines,Part 5

Aliphatic nitro compounds can be considered as good precursors of a wide variety of α‐azolyl‐substituted oximes. The double silylation of convenient aliphatic nitro compounds and the subsequent N,C‐coupling of the resulting N,N‐bis(silyloxy)enamines 3 with N‐silylated azoles 4 lead to the formation of the silylated α‐azolyl‐substituted oximes 6 , which can be smoothly desilylated to give the target α‐azolyl‐substituted oximes 5 . The mechanism of the key step of this process – N,C‐coupling – includes the generation of corresponding conjugated nitrosoalkenes 7 (Schemes 4 and 5). The contribution of the chain mechanism in the overall process is considered as well. The studies of the scope and limitations of this reaction, as well as the optimization of its conditions were accomplished. The configuration of the CN bond in oximes was established by NMR.     

Comparative analysis of 13C shielding constants stereospecificity in the silicon and germanium derivatives of acetylenic aldehyde and ketone oximes based on the 13C NMR spectroscopy and GIAO calculations

In the acetylenic aldehyde oximes with substituents containing silicon and germanium, the ¹³C NMR signal of the C‐2 carbon of triple bond is shifted by 3.5 ppm to lower frequency and that of the C‐3 carbon is moved by 7 ppm to higher frequency on going from E to Z isomer. A greater low‐frequency effect of 5.5 ppm on the C‐2 carbon signal and a greater high‐frequency effect of 11 ppm on the C‐3 carbon signal are observed in the analogous acetylenic ketone oximes. The carbon chemical shift of the C?N bond is larger by 4 ppm in E isomer relative to Z isomer for the aldehyde and ketone oximes. The ²⁹Si chemical shifts in the silicon containing acetylenic aldehyde and ketone oximes are almost the same for the diverse isomers. The trends in changes of the measured chemical shifts are well reproduced by the gauge‐including atomic orbital (GIAO) calculations of the ¹³C and ²⁹Si shielding constants. Copyright © 2009 John Wiley & Sons, Ltd.