Showing papers by "Alan R. Katritzky published in 1980"
TL;DR: The pyrylium cations with substitution patterns more strictly demanding than 2,4,6-triphenyl and these are examined as reagents for the conversion of primary into a leaving group.
Abstract: Efficient syntheses are developed for several pyrylium cations with substitution patterns more strictly demanding than 2,4,6-triphenyl and these are examined as reagents for the conversion of primary into a leaving group, The 2-mesityl-4,6-diphenyl derivative did not react smoothly with amines. The 2,6-di-t-butyl-4-phenyl-pyrylium cation gave the corresponding pyridinium derivatives, but they resisted nucleophillic attack 2-t-butyl-4,6-diphenylpyridinium cations suffer nucleophilic attack with about the same case as the 2,4,6-triphenyl analogues. Dihydrobenzopyrylium (6) and tetrahydrodibenzoxanthylium cations (7) gave pyridinium cations which underwent much easier nucleophilic attack: thus they alkylate xanthate anion in ethanol solution and acetate anion in acetic acid.
32 citations
TL;DR: In this paper, four novel rearrangements of derivatives of 1-hydroxy-4,6-diphenyl-2-pyridone are reported: all involve homolytic N-O fission and formation of 3-substituted or both 3- and 5-substantituted-4-6-diagrams-of-1.
Abstract: Examples of four novel rearrangements of derivatives of 1-hydroxy-4,6-diphenyl-2-pyridone are reported: all involve N–O fission and formation of 3-substituted or both 3- and 5-substituted-4,6-diphenyl-2-pyridones. (a) 1-OCH2CH2R (R = vinyl or phenyl) compounds give 3-CH2R (R = vinyl or phenyl) derivatives with elimination of CH2O. (b) The 1-octyloxy-compound gives the 3-octyloxy-derivative by simple transposition. (c) 1-Acyloxy-compounds form the corresponding 3- and 5-acyloxy-2-pyridones. (d) 1-Imidoyloxy-compounds yield the rearranged 3-and 5-amido-2-pyridones. The mechanisms probably all involve homolytic N–O fission.
20 citations
TL;DR: In this paper, N-(2,6-Dimethyl-4-oxopyridin-1-yl)pyridine salts were used for the regiospecific synthesis of 4-substituted pyridines.
Abstract: N-(2,6-Dimethyl-4-oxopyridin-1-yl)pyridinium salts (4), new reagents for the regiospecific synthesis of 4-substituted pyridines, give moderate to high yields of 4-alkyl- and 4-aryl-pyridines (8)–(10) on reaction with Grignard reagents. The scope and limitations of the reaction, which proceeds via 1,4-dihydro-intermediates (5)–(7), are explored. No 2-substituted pyridines were detected. Some reactions with organolithium compounds are also described.
18 citations
TL;DR: For example, 1-Alkyl-1-2-dihydropyridines thermolyse to complex mixtures, but 1-alkyl-2,3,5,6-tetraphenyl-1,4-dibyridine gives ω-monodeuteriotoluene (as shown by 2H n.m.r. spectroscopy) indicating a radical mechanism as mentioned in this paper.
Abstract: 1-Alkyl-1,2-dihydropyridines thermolyse to complex mixtures, but 1-alkyl-2,3,5,6-tetraphenyl-1,4-dihydropyridines (prepared from the amine and 2,3,5,6-tetraphenylpyrylium salts followed by NaBH4) give alkanes smoothly at ca. 200 °C.Thermolysis of 1-benzyl-2-deuterio-2,4,6-triphenyl-1,2-dihydropyridine gives ω-monodeuteriotoluene (as shown by 2H n.m.r. spectroscopy) indicating a radical mechanism.
15 citations
Abstract: Conformational equilibria and barriers to ring and nitrogen inversion are determined by 1H and 13C n.m.r. for 13 1-oxa-3-azacyclohexanes and correlated with recent work on the conformational analysis of saturated heterocycles.
14 citations
TL;DR: In this article, N-Alkyl- and N-benzyl-4-p-chlorophenyl-2,3,5,6-tetraphenyl-N-alkyl-and N-Benzyl -2, 3, 4, 5, 6, 6-pentaphenyl-, and n-hexyl-pyridinium bromides on pyrolysis at 180-220 °C gave the corresponding n-octyl bromide (80%) was obtained from the corresponding pentacyclic
Abstract: N-Alkyl- and N-benzyl-4-p-chlorophenyl-2,3,5,6-tetraphenyl-N-alkyl- and N-benzyl-2,3,4,5,6-pentaphenyl-, and N-alkyl- and N-benzyl-2,4,6-triphenyl-pyridinium bromides on pyrolysis at 180–220 °C give the corresponding alley and benzyl bromides in high yield. 1-Benzyl-5,6-dihydro-2,4-diphenylbenzo[h]quinolinium trifluoromethanesulphonate gave benzyl bromide on heating with KBr in dimethylformamide at 100 °C, and n-octyl bromide (80%) was obtained from the corresponding pentacyclic bromide in refluxing acetonitrile.
14 citations
TL;DR: The site-, regio-, and stereo-selectivity of these cycloadditions are discussed with reference to MO predictions in this article, where the β-aroylvinyl substituents in the adducts can be hydrolytically removed.
Abstract: β-p-Chloro-, β-p-bromo-, and β-2-chloro-5-nitrobenzoyl-vinyl chloride react with 3-hydroxypyridine to give quaternary salts which with base give the corresponding betaines. These betaines undergo thermal dimerisation and cycloadditions with mono- and di-enes at the 2,6- and 2,4-positions, respectively. The site-, regio-, and stereo-selectivity of these cycloadditions are discussed with reference to MO predictions. The β-aroylvinyl substituents in the adducts can be hydrolytically removed.
13 citations
TL;DR: In this article, N-Alkyl and N-benzyl substituents are displaced from 2,4,6-triphenylpyridinium rations by nucleophilic azide, phthalimide, succinimide and sulphonamide anions.
Abstract: N-Alkyl and N-benzyl substituents are displaced from 2,4,6-triphenylpyridinium rations by nucleophilic azide, phthalimide, succinimide, and sulphonamide anions. This enables the conversion of primary alkyl- and benzylamines into azides, and primary (with potential for inversion or labelling) and secondary amines.
13 citations
TL;DR: In this article, the Frontier-MO theory is used to rationalise the orientation of these cycloadditions, resulting in 3-hydroxy-2-benzylpyridines.
Abstract: Dichloroketen and a series of aryl(bromo)ketens react with various 1-substituted 3-oxidopyridiniums to give novel bicyclic compounds by addition across the C(4)–O and the C(2)–O positions. Frontier-MO theory is used to rationalise the orientation of these cycloadditions. Acid-catalysed hydrolysis of the C(2)–O adducts (9) yielded 3-hydroxy-2-benzylpyridines.
11 citations
TL;DR: Conformational equilibria and barriers to ring and nitrogen inversion, determined by 1H and 13C n.m.r. for the title compounds, are correlated with other recent work on ring-1,3-diheteroatom-substituted cyclohexanes as mentioned in this paper.
Abstract: Conformational equilibria and barriers to ring and nitrogen inversion, determined by 1H and 13C n.m.r. for the title compounds, are correlated with other recent work on ring-1,3-diheteroatom-substituted cyclohexanes.
10 citations
TL;DR: In this article, 1-Benzyl-4,6-diphenyl-2-pyridone is lithiated by LiNPrI2 at the methylene carbon to form a carbanion which reacts with various electrophiles to give the corresponding 1-(α-substituted-benzyl)-4, 6-diminear-2 pyridones.
Abstract: 1-Benzyl-4,6-diphenyl-2-pyridone is lithiated by LiNPrI2 at the methylene carbon to form a carbanion which reacts with various electrophiles to give the corresponding 1-(α-substituted-benzyl)-4,6-diphenyl-2-pyridones. Potassium dimsylate converts 1-benzyl-4,6-diphenyl-2-pyridone into the 3-methyl derivative. The anion derived from 1-(α-methylbenzyl)-4,6-diphenyl-2-pyridone rapidly rearranges to the azepinone (18).
TL;DR: The triazinyl betaines as discussed by the authors undergo spontaneous thermal dimerisation, and all add a variety of 2π, 4π, and/or 6π dipolarophiles.
Abstract: The title betaines are prepared: the two triazinyl betaines undergo spontaneous thermal dimerisation, and all add a variety of 2π, 4π, and/or 6π dipolarophiles. The regio- and stereo-chemistry of the addition are elucidated and rationalised. The pyridyl adducts undergo quaternisation and ring opening to tropolones.
TL;DR: The pyridinium fluorides are made from 2,4,6-triphenyl-pyrylium fluoride and the relevant amine as discussed by the authors, and they thermolyse to the corresponding primary alkyl and benzyl fluorides.
Abstract: N-Substituted 2,4,6-triphenylpyridinium fluorides (in contrast to these and other tetrafluoroborates) thermolyse to the corresponding primary alkyl and benzyl fluorides. The pyridinium fluorides are made from 2,4,6-triphenyl-pyrylium fluoride and the relevant amine.
TL;DR: In this paper, the title cation abstracts hydride from aliphatic amines yielding the corresponding thiopyran: with methylamine some pyridinium cation was also found.
Abstract: The title cation abstracts hydride from aliphatic amines yielding the corresponding thiopyran: with methylamine some pyridinium cation is also found. With aniline, and its N- and ring-substituted and hetero-analogues, fair yields of novel thiopyrylium dyes are obtained.
TL;DR: In this article, 1-substituted 2-and -4-methylpyridinium cations are converted by pentyl or ethyl nitrite and sodium methoxide into 1substitized 2- and 4-pyridine cations respectively.
Abstract: 1-Substituted 2- and -4-methylpyridinium cations are converted by pentyl or ethyl nitrite and sodium methoxide into 1-substituted-2- and -4-pyridones respectively.
TL;DR: In this paper, the conformational equilibria and kinetic interconversions for 1,3,4-thiadiazacyclohexanes were investigated in 1H and 13C n.m.r. spectra.
Abstract: Variable temperature 1H and 13C n.m.r. spectra elucidate the conformational equilibria and kinetic interconversions for 1,3,4-thiadiazacyclohexanes. The results are compared with those of analogous compounds and the effect of the sulphur atom discussed.
TL;DR: In this paper, a pyrolysed pyridinium thiocyanates with a KNCS-NaCNS eutectic at ca. 220 °C give the aryl thiocyyanates in yields averaging 80%.
Abstract: 5,6-Dihydro-2,4-diphenylnaphtho[1,2-b]pyrylium thiocyanate is prepared in high yield. It reacts with primary arylamines to yield the corresponding fused pyridinium thiocyanates which when pyrolysed with a KNCS–NaCNS eutectic at ca. 220 °C give the aryl thiocyanates in yields averaging 80%.
TL;DR: The 1,4-dimethyl-2,5-dibenzyl monocycle (2), unsaturated tricycle (3), and saturated tricycle(4) exist in the crystal in the aeae, ae3, and e4 conformations, respectively as mentioned in this paper.
Abstract: The 1,4-dimethyl-2,5-dibenzyl monocycle (2), the unsaturated tricycle (3), and the saturated tricycle (4) exist in the crystal in the aeae, ae3, and e4 conformations, respectively. The conformation behaviour is compared with that in solution and the molecular dimensions with those of similar compounds. The conformations deduced by n.m.r. spectroscopy for solutions are generally those found for the crystals.
TL;DR: In this paper, it was shown that 1,2,4,5-tetra-azacyclohexanes and 3,4-dimethyl-1-thia-3, 4, 4-diaza-cyclohexane (4) probably exist in the αIµα and I µα conformations, respectively.
Abstract: 2-Oxa-4a,8a-diazadecalin (2) shows bands of the predominant αα and a minor Iµα form. 1,2,4-Trimethyl-1,2,4-triaza-(3) and 3,4-dimethyl-1-thia-3,4-diaza-cyclohexane (4) probably exist in the αIµα and Iµα conformations, respectively. These conclusions are in good agreement with those from solution measurements, as are those for four 1,2,4,5-tetra-azacyclohexanes.
TL;DR: The chemical identities of (6b), (11 c), and (13) were elucidated by an X-ray diffraction study, although each exhibits some conformational disorder in the crystalline state, associated with a rotation of the hydroxyphenyl moiety as discussed by the authors.
Abstract: Isonitrosoflavanone toluene-p-sulphonate reacts with Schiff bases to form (o-hydroxybenzoyl)imidazoles (6); in one case the regioisomeric pyrazole (10) was also isolated. Analogous reactions occur with pyridine and its methyl- and benzo-derivatives to form pyridoimidazoles [cf. (11)].The chemical identities of (6b), (11 c), and (13) were elucidated by an X-ray diffraction study, although each exhibits some conformational disorder in the crystalline state, associated with a rotation of the hydroxyphenyl moiety. The hydroxy-group can intramolecularly hydrogen-bond with either the carboxylate oxygen atom or the imidazo-moiety nitrogen. In compounds (6b) and (13) the hydroxy-group is primarily H-bonded to the oxygen, and in (11c) to the nitrgen.
TL;DR: In this paper, the addition of N-(2,6-dimethyl-4-oxopyridin-1-yl)pyridine salts to tetrahydrofuran at low temperatures gives regiospecifically high yields of 1,4-dihydro-adducts (5) and αβ-unsaturated ketones, however, give products resulting from reaction exclusively at the position α′ to the carbonyl group.
Abstract: The addition of N-(2,6-dimethyl-4-oxopyridin-1-yl)pyridinium salts (2)–(4) to lithium enolates (1) of ketones in tetrahydrofuran at low temperatures gives regiospecifically high yields of 1,4-dihydro-adducts (5)–(7). These are readily isolated and can be decomposed under free-radical conditions, also in high yield, to 4-(α-acylalkyl)pyridines (8)–(10). Unsymmetrical dialkyl ketones give a mixture of two isomeric products, the ratio depending upon reaction conditions and steric factors. αβ-Unsaturated ketones, however, give products resulting from reaction exclusively at the position α′ to the carbonyl group.
TL;DR: In this paper, 1-Hetero-3-oxidopyridinium dimers with dienamines give cycloadducts which are dehydrogenated to mixed dimers.
Abstract: 1-Heteroaryl-3-oxidopyridinium dimers with dienamines give cycloadducts which are dehydrogenated to ‘mixed dimers’ of the corresponding 2-heteroaryl-4-oxidoisoquinolinium with the starting 1-heteroaryl-3-oxidopyridinium. The ‘mixed dimer’(21) is also effectively prepared by a two-step sequence of a novel intramolecular oxidation–reduction, followed by oxidation of the resulting alcohol. The ‘mixed dimers’ undergo reversible thermal dissociation and in one case the corresponding monomers could be trapped as various cycloadducts.
TL;DR: The Conformational Analysis of Heterocyclic Compounds by Frank Riddell as discussed by the authors is a seminal work in the field of homology analysis and homology research. Pp. 153.
Abstract: The Conformational Analysis of Heterocyclic Compounds. by Frank Riddell. Pp. 153. (Academic: London and New York, 1980.) £17, $39.50.