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Showing papers in "Journal of The Chemical Society-perkin Transactions 1 in 1987"


Journal ArticleDOI
TL;DR: The average lengths of bonds involving the elements H, B, C, N, O, F, Si, P, S, Cl, As, Se, Br, Te, and l in organic compounds are reported in this article.
Abstract: The average lengths of bonds involving the elements H, B, C, N, O, F, Si, P, S, Cl, As, Se, Br, Te, and l in organic compounds are reported.

6,649 citations


Journal ArticleDOI
TL;DR: In this paper, the p-nitrocalixarenes were used as intermediates in the synthesis of a variety of functionalised calixarene-p-sulphonates (tetramer, hexamer, and octamer).
Abstract: Calixarene-p-sulphonates (tetramer, hexamer, and octamer) have been prepared (75–88%) and used to give p-nitrocalixarenes (15–22% yields based on the starting calixarenes). The novel nitration has two advantages: (i) calixarenes are protected from nitric acid oxidation by the electron-withdrawing sulphonate groups and (ii) the difference in the water-solubility of the p-nitrocalixarenes from the sulphonate-containing, lower nitration products, allows ready isolation of the former. The p-nitrocalixarenes thus obtained have potential as intermediates in the synthesis of a variety of functionalised calixarenes.

186 citations


Journal ArticleDOI
TL;DR: Olive oil-water partition coefficients, Loil, have been determined for 80 solutes at 310 K using a gas chromatographic method in which olive oil is used as the stationary phase as discussed by the authors.
Abstract: Olive oil–gas partition coefficients, Loil, have been determined for 80 solutes at 310 K using a gas chromatographic method in which olive oil is used as the stationary phase. Combination with other literature values has enabled a list of 140 log Loil values at 310 K to be constructed. Hexadecane–gas partition coefficients, Lhex, have similarly been determined for 140 solutes at 298 K. It is shown that olive oil–water partition coefficients, Poil, calculated indirectly from Loil and Lwater partition coefficients agree quite well with directly determined Poil values. Similarly, hexadecane–water partition coefficients, Phex, obtained from Lhex and Lwater agree with directly determined values. It is suggested that in the case of the two particular solvents, olive oil and hexadecane, mutual miscibility of the two phases is of little consequence, and that Poil and Phex values can conveniently be obtained by combining the respective solvent–gas and water–gas partition coefficients.

164 citations


Journal ArticleDOI
TL;DR: In this paper, the condensation of a chiral N-protected amino acid with Meldrum's acid in the presence of isopropenyl chloroformate (IPCF) and of 4-N,N-dimethylaminopyridine (DMAP) has been examined.
Abstract: The condensation of a chiral N-protected amino acid with Meldrum's acid in the presence of isopropenyl chloroformate (IPCF) and of 4-N,N-dimethylaminopyridine (DMAP) has been examined. The cyclisation of the reaction product, by heating in an organic solvent, gave the N-protected tetramic acid derivatives (4a–i) which, after reduction, afforded the corresponding threo-4-hydroxypyrrolidin-2- ones (5a–i). The regioselective alkaline or acid hydrolysis of the N-protected pyrrolidin-2-ones led to enantiomeric pure N- Boc-statine (6a) and its analogues (6b–i) in 40–60% yield from the N-protected amino acids. The corresponding statine methyl esters (7a–i) could also be synthesized in high yield.

158 citations


Journal ArticleDOI
TL;DR: In this paper, the 13C n.m.r.1 H and 13C N.m R N. r. spectra for all mono-O-acetyiated methyl α- and β-glycopyranosides of D-glucose and D-galactose were obtained and compared with those of the corresponding non-acetylated derivatives.
Abstract: 1 H and 13C N.m.r. spectra for all mono-O-acetyiated methyl α- and β-glycopyranosides of D-glucose and D-galactose were obtained and compared with those of the corresponding non-acetylated derivatives. It is shown that the 13C n.m.r. chemical shifts of the carbons in positions α and β to an O-acetyl group can be approximated using simple rules, for which the number and location of eventual axial substituents are essential. The chemical shifts of the α- and β-protons are in the same way sensitive to axial substituents. Furthermore the conformation of the O-acetyl group was assessed by measurements of 3JC,C and 3JC,H of some selected O-acetates, 13C-enriched in the carbonyl carbon, and by theoretical energy calculations.

137 citations


Journal ArticleDOI
TL;DR: In this article, the reaction of HRh(CO)2(PPh3)3(1) with CO has been studied by 1H, 13C, and 31P n.m.
Abstract: The reaction of HRh(CO)(PPh3)3(1) with CO has been studied by 1H, 13C, and 31P n.m.r. The main species present under ambient conditions is HRh(CO)2(PPh3)2(2) which exists as two rapidly equilibrating trigonal bipyramidal isomers. Complexes (1) and (2) are in rapid equilibrium via CO and PPh3 dissociation steps and the square-planar complexes HRh(CO)(PPh3)2(3) and HRh(CO)2PPh3(4) are likely transient intermediates. The chemistry of these PPh3 complexes is compared with that of closely related 5-phenyl-5H-dibenzophosphole and 1,3-bis(diphenylphosphino)propane analogues. Complex (1) catalyses the isomerisation of (Z)-[1,2-2H2]styrene, effectively suppressed by CO or PPh3. HRh(CO)2P2 complexes trap methylenecyclopropane. In the presence of styrene and CO, complex (1) is converted into a branched acyl derivative which readily equilibrates with its linear isomer; the stereochemistry of these acyl derivatives (CO)2(PPh3)2RhCOR is determined by low-temperature n.m.r.; at higher temperatures rapid inter- and intra-molecular exchange processes occur. The relevance of these observations to rhodium-catalysed hydroformylation is discussed and it is proposed that the regiochemistry of reaction is largely controlled by competitive olefin trapping involving complexes (3) and (4).

120 citations


Journal ArticleDOI
TL;DR: The Mammea coumarins of the 4-phenyl-(mammea A), 4-propyl(mammmea B), and 4-pentyl-(naphyl)-mammmea C) series have been prepared by Pechmann condensation of an acylphloroglucinol with the appropriate β-ketoester to give a mixture of 6- and 8-acyl-5,7-dihydroxycoumarins that could be separated C-Alkylation with 3-methylbut
Abstract: The naturally-occurring Mammea coumarins of the 4-phenyl-(mammea A), 4-propyl-(mammea B), and 4-pentyl-(mammea C) series have been prepared by Pechmann condensation of an acylphloroglucinol (3-methylbutyryl-, 2-methylbutyryl-, butyryl-, or 2-methylpropionyl-) with the appropriate β-ketoester to give a mixture of 6- and 8-acyl-5,7-dihydroxycoumarins that could be separated C-Alkylation with 3-methylbut-2-enyl bromide, or 3,7-dimethylocta-2,6-dienyl chloride, in aqueous potassium hydroxide completed the synthesis of the Mammea coumarins having unmodified prenyl or geranyl substituents; oxidative modification of the prenyl group led to the mammea cyclo E and cyclo F coumarins Some mammea cyclo D (chromeno) coumarins were synthesized by reaction of acylcoumarins with 1,1-dimethoxy-3-methylbutan-3-ol

117 citations


Journal ArticleDOI
TL;DR: In this article, the authors calculated the hyperpolarisabilities of the symmetrical polyphenyls, containing an electrondonating dimethylamino group and an electron-attracting nitro group positioned at opposite ends of the conjugated system, slowly increase with an increasing number of phenyl units.
Abstract: The calculated hyperpolarisabilities of the symmetrical polyphenyls, containing an electron-donating dimethylamino group and an electron-attracting nitro group positioned at opposite ends of the conjugated system, slowly increase with an increasing number of phenyl units, but the effect per unit volume is a maximum for 4-dimethylamino-4′-nitroterphenyl. In contrast, the calculated values for polyenes containing the same donor and attractor increase rapidly with an increasing number of ethenyl units, and the effect per unit volume is a maximum for 20 units. Overall, the polyene system shows an effect which is at least 20 times that of the polyphenyl system and 10 times that of any other known system. A similar effect is also found in the dimethylaminopolyenals, though a comparison between calculated and experimental dipole moments and electronic transition energies suggests that their hyperpolarisabilities may be somewhat overestimated at the CNDO level of approximation.

95 citations


Journal ArticleDOI
TL;DR: In this article, the marine adhesive polydecapeptide (Ala-Lys-Pro-Ser-Tyr-Hyp-Hyp Hyp-Thr-Dopamine-Dopa)-Lys)n(n ca. 10) has been synthesized by coupling reactions, followed by polycondensation.
Abstract: The marine adhesive polydecapeptide (Ala-Lys-Pro-Ser-Tyr-Hyp-Hyp-Thr-Dopa-Lys)n(n ca. 10) has been synthesized by coupling reactions, followed by polycondensation. The O-benzyl, O,O′-dibenzyl, and N-Iµ-2-chlorobenzyloxycarbonyl groups were used to protect the side chains of Ser, Tyr, Hyp, Thr, Dopa, and Lys. The protecting groups were simultaneously cleaved by hydrogen bromide. The bonding strength of the polydecapeptide and other synthetic polypeptides on metals has been measured in water. The bonding strength of the synthesized polydecapeptide exhibited a tensile strength of 28 kg cm–1 on Fe and a compressive shear strength of 3 kg cm–2 on Al2O3, while high molecular weight poly(Lys)·HBr was found to have the highest tensile strength (123 kg cm–2) on Fe, and gelatin the highest compressive shear strength (21 kg cm–2) on Al2O3. The factors important for the effective adhesion on metals are discussed.

85 citations


Journal ArticleDOI
TL;DR: In this article, an asymmetric ring-opening of prochiral acid anhydrides with methanol has been achieved by a catalytic quantity of cinchona alkaloids.
Abstract: Asymmetric ring-opening of prochiral acid anhydrides (1) with methanol has been achieved by a catalytic quantity of cinchona alkaloids (2). The product, the optically active half-ester (3), has been subjected to functional-group-selective reduction to give the optically active lactones (5). The reaction rate of the ring-opening and the extent of selectivity are dependent on the nature of the reaction medium, the polarity of solvent, and substrate concentration. By selecting the reaction conditions, an enantiometric excess of up to 70% has been obtained. The kinetic isotope effect and other mechanistic investigations suggest that the reaction proceeds via general-base catalysis by the quinuclidine moiety of the base (2), and that the relative configuration of the C-9 hydroxy group with respect to the C-8 quinuclidine amino function determines the selectivity of the reaction.

83 citations


Journal ArticleDOI
TL;DR: The synthesis, colour, and constitution of methine dyes formed by condensation of benzaldehydes and nitrosobenzenes with dicyanovinyl analogues of indane-1,3-dione have been investigated.
Abstract: The synthesis, colour, and constitution of methine dyes formed by condensation of benzaldehydes and nitrosobenzenes with dicyanovinyl analogues of indane-1,3-dione have been investigated. 3-Dicyanovinylindan-1-one (3) and 1,3-bisdicyanovinylindane (5) give magenta (λmax.ca. 560 nm) and blue (λmax.ca. 600 nm) dyes respectively with 4-dialkylaminobenzaldehydes. Aza analogues formed from (3) and (5) and 4-dialkylaminonitrosobenzenes are significantly more bathchromic, and the exceptional shift in the case of dyes formed from (5)(ca. 150 nm) permits the synthesis of a new class of dyes absorbing in the near-i.r. region, with absorption maxima in the range 700–850 nm.

Journal ArticleDOI
TL;DR: In this article, it was shown that a trifluoroethanol-ethanol plot, wherein ButCl and 1-adamantyl chloride (1-AdCl) solvolysis rates are compared, can be interpreted as evidence for electrophilic assistance of ButCl in TFE rather than the more usual interpretation of nucleophilic assistance to ButCl, in EtOH-H2O.
Abstract: Solvolysis/dehydrohalogenation rates of t-butyl chloride in 21 hydrogen bond donor (HBD) and non-HBD solvents are well correlated (r= 0.9973, s.d. = 0.24) by the equation: log k=–14.60 + 0.48λH2/100 + 5.10π*+ 4.17α+ 0.73β where δH2 is the solvent cohesive energy density, and π*, α, and β are the solvatochromic parameters that scale solvent diplority–polarizability, HBD acidity (electrophilicity), and hydrogen-bond acceptor basicity (nucleophilicity). In the corresponding equation over the same solvent set for t-butyl bromide, the terms in δH2 and α are smaller still, and the terms in δH2 and β are not statistically significant. It is shown that a trifluoroethanol (TFE)–ethanol plot, wherein ButCl and 1-adamantyl chloride (1-AdCl) solvolysis rates are compared, can be interpreted as evidence for electrophilic assistance of 1-AdCl in TFE rather than the more usual interpretation of nucleophilic assistance to ButCl in EtOH–H2O.

Journal ArticleDOI
TL;DR: In this paper, S-t-butyl acetothioacetate derivatives were cyclised efficiently to acyltetronic acid derivatives using tetrabutyl ammonium fluoride in THF solution at room temperature.
Abstract: Dianions generated from S-t-butyl acetothioacetate (1) were alkylated with a variety of electrophiles at the γ-carbon centre. Treatment of the alkylated products with 2-hydroxy esters in the presence of silver(I) salts gave transesterified acetoacetate derivatives in good yields. These acetoacetates were cyclised efficiently to acyltetronic acid derivatives using tetrabutyl ammonium fluoride in THF solution at room temperature. By an appropriate choice of substituents the total syntheses of the fungal metabolite natural products carlosic, carolic, and carlic acids have been achieved.

Journal ArticleDOI
TL;DR: In this article, the N-chloromethyl group of 1-(Chamberlainhyl)benzotriazole undergoes nucleophilic substitution by carbon, nitrogen, phosphorus, oxygen, and sulphur nucleophiles.
Abstract: The N-chloromethyl group of 1-(chloromethyl)benzotriazole undergoes nucleophilic substitution by carbon, nitrogen, phosphorus, oxygen, and sulphur nucleophiles. α-Lithiation was achieved in high yield in 1-phenylthiomethyl-, 1-phenylsulphinylmethyl-, and 1-(phenylstilphonylmethyl)benzotriazoles and the lithio derivatives reacted with a variety of electrophiles. New benzotriazolium salts were prepared by quaternization of the N-3 nitrogen with methyl iodide.

Journal ArticleDOI
TL;DR: Syntheses of the piperolides, the fadyenolides and epoxypiperolide, and related compounds are described in this paper, where Narthogenin is also efficiently produced.
Abstract: Syntheses of the piperolides, the fadyenolides, epoxypiperolide, and related compounds are described. (±)-Narthogenin is also efficiently produced.

Journal ArticleDOI
TL;DR: In this paper, condensations between ethyl 4-bromo-3-oxohexanoate and acyl phloroglucinols, 5- or 7-acyl benzo[b]furans were isolated rather than the desired 4-(1-acetoxypropyl)-5,7-dihydroxy-6(or 8)-acylcoumarins, or 6- or 8-acylfuro[4,3,2,d,e][1]benzopyran-4(2H)-
Abstract: From condensations between ethyl 4-acetoxy-3-oxohexanoate and acyl phloroglucinols, 5- or 7-acyl benzo[b]furans (5) were isolated rather than the desired 4-(1-acetoxypropyl)-5,7-dihydroxy-6(or 8)-acylcoumarins. Related condensations between ethyl 4-bromo-3-oxohexanoate, or ethyl 4-chloro-3-oxobutanoate, and acyl phloroglucinols afforded either the desired 4-(1-haloalkyl)-5,7-dihydroxy-6(or 8)-acylcoumarins, or 6- or 8-acylfuro[4,3,2,-d,e][1]benzopyran-4(2H)-ones (11) by subsequent dehydrohalogenation. Attempted conversion of the 4-(1-haloalkyl)coumarins into 4-(1-acetoxyalkyl)coumarins with sodium acetate–acetic acid gave acylbenzofurans (5), with silver acetate in acetonitrile gave acylfurobenzopyranones (11) and with tetramethylammonium acetate gave the isomeric acylfurobenzopyranones (13). Allyiic bromination of 6-butyryl-5,7-dimethoxy-4-propylcoumarin and conversion of the 4-(1-bromopropyl) product to a 4-(1-acetoxypropyl)coumarin, followed by a difficult demethylation and subsequent C-prenylation afforded mammea E/AC, a 6-acyl isomer of one of the natural 8-acyl insecticidal Mammea coumarins; application of this sequence to 8-butyryl-5,7-dimethoxy-4-propylcoumarin failed at the demethylation stage.

Journal ArticleDOI
TL;DR: In this article, inorganic arsenic has been reported to be present in the seaweed Hizikia fusiforme as a pair of C-2 diastereoisomers.
Abstract: (2S)-3-[5-Deoxy-5-(dimethylarsinoyl)-β-D-ribofuranosyloxy]-2-hydroxypropyl hydrogen sulphate (1a), 3-[5-deoxy-5-(dimethylarsinoyl)-β-D-ribofuranosyloxy]-2-hydroxypropene-1-sulphonic acid (1b), 1-‘glycerophosphoryl’-2-hydroxy-3-[5-deoxy-5-(dimethylarsinoyl)-β-ribofuranosyloxy]propane (1c), and 2-amino-3-[5-deoxy-5-(dimethylarsinoyl)-β-D-ribofuranosyloxy]propene-1-sulphonic acid (1d), together with inorganic arsenic have been isolated from the edible seaweed Hizikia fusiforme. Structures have been determined chiefly by n.m.r. spectroscopy. Compound (1d) has not been reported previously. Compound (1b) is apparently present in Hizikia as a pair of C-2 diastereoisomers.

Journal ArticleDOI
TL;DR: In this paper, the thermal stability of α-fluoromethanephosphonate carbanions decreases in the series CHF > CF2 > CFCl, where CF2 = CFCl.
Abstract: The thermal stability of α-fluoromethanephosphonate carbanions decreases in the series CHF > CF2 > CFCl. Acylation products of the difluoromethanephosphonate carbanion show high electrophilic reactivity which results in the immediate formation of secondary products. This behaviour is not observed for the monofluoromethanephosphonate carbanion. Attempts to acylate or phosphorylate the chiorofluoromethanephosphonate carbanion unexpectedly provide esters of fluoromethylenebisphosphonic acid as products. Some physical characteristics of fluoromethanephosphonic acids are described.

Journal ArticleDOI
TL;DR: 1-(1-Hydroxyalkyl)benzotriazoles convert a wide variety of aromatic and heteroaromatic primary amines into their mono N-[1-(benzOTriazol-1-yl)alkyl] derivatives in high yield in highield.
Abstract: 1-(1-Hydroxyalkyl)benzotriazoles convert a wide variety of aromatic and heteroaromatic primary amines into their mono N-[1-(benzotriazol-1-yl)alkyl] derivatives in high yield. Aliphatic primary amines frequently give bis-derivatives. Product structure is established by 13C n.m.r.; dangers in the use of 1H n.m.r. to distinguish 1- and 2-substituted benzotriazoles are pointed out.

Journal ArticleDOI
TL;DR: In this article, a stepwise solid phase method using 1% crosslinked Merrifield resin and benzotriazolyloxyloxytris(dimethylamino)phosphonium hexafluorophosphate (BOP reagent) respectively as solid support and coupling reagent was used.
Abstract: A successful synthesis of Asp1-Arg2-Val3-Tyr4-IIe5-His6-Pro7-Phe6-His9-Leu10-Leu11-Tyr12-Tyr13-Ser14 has been achieved by the classical stepwise solid-phase method using 1% crosslinked Merrifield resin and benzotriazolyloxytris(dimethylamino)phosphonium hexafluorophosphate (BOP reagent) respectively as solid support and coupling reagent. The coupling protocol included in situ neutralization of the amino partners after Boc-deprotection and the coupling times seldom exceeded 30 min. For His6 and His9, Boc-His(Boc). DCHA was neutralized in situ and allowed to couple. The peptide, purified by reparative h.p.l.c., was obtained in 29% overall yield based on the first residue attached to the solid support.

Journal ArticleDOI
TL;DR: Intermolecular interactions in CH/π systems have been studied by PCILO and ab initio MO methods to elucidate the origin of the attractive interactions as discussed by the authors, where the van der Waals molecules of CH4+ C2Hn(n= 2 or 4) were more stable than that of CH 4+ C 2H6, and the most stable arrangement was such that the carbon atom in methane is shifted from the C2 axis perpendicular to the C-C-H plane of ethene.
Abstract: Intermolecular interactions in CH/π systems have been studied by PCILO and ab initio MO methods to elucidate the origin of the attractive interactions. In the PCILO calculations, the van der Waals molecules of CH4+ C2Hn(n= 2 or 4) were more stable than that of CH4+ C2H6, and the most stable arrangement was such that the carbon atom in methane is shifted from the C2 axis perpendicular to the C–C–H plane of ethene. Ab initio MO results supported this conclusion and showed also that the main contributions to attractive CH/π interactions come from electrostatic and charge-transfer effects. These results were supported by electrostatic-potential maps of C2H4 and C2H6.

Journal ArticleDOI
TL;DR: In this article, the most efficient treatment of phosphonate esters with iodine in pyridine-water was investigated under various reaction conditions, and the most likely pathway for the majority of the oxidations was proposed.
Abstract: Oxidation of phosphonate mono- and di-esters with various oxidizing agents including diaryl disulphides, hexachloroacetone, and iodine, has been investigated under various reaction conditions. The most efficient oxidation procedure consists of treatment of phosphonate esters with iodine in pyridine–water. When the phosphonate esters were presilylated by treatment with trimethylsilyl chloride, the subsequent oxidation with aqueous iodine was faster. 31P N.m.r. spectroscopic studies have enabled us to propose the most likely pathway for the majority of the oxidations.

Journal ArticleDOI
TL;DR: In this paper, demethylaaptamine (2) and demethyl(oxy)aaptamines (3) have been isolated from the Okinawan marine sponge Aaptos aaptos as cytotoxic and antimicrobial substances.
Abstract: Two new a apptamine alkaloids, demethylaaptamine (2) and demethyl(oxy)aaptamine (3), have been isolated from the Okinawan marine sponge Aaptos aaptos as cytotoxic and antimicrobial substances. The structures of demethylaaptamine (2) and demethyl(oxy)aaptamine (3) were determined by interpretation of spectral data and results of chemical degradation experiments.

Journal ArticleDOI
TL;DR: In this paper, 1,2,4,5-di-O-isopropylidene-myo-inositol was converted into 1.2,3,4-Tetra-O-, O-p-methoxybenzyl-myon-inotol, using allyl groups for temporary protection, and two monoallyl and monoprop-1-enyl ethers were also prepared as model compounds for phosphorylation studies of the vicinal 5,6-diol system.
Abstract: Racemic 1,2:4,5-di-O-isopropylidene-myo-inositol was converted into racemic 1,2,4-tri-O-benzyl-myo-inositol, 1,2,4-tri-O-p-methoxybenzyl-myo-inositol and 2,4,5-tri-O-benzyl-myo-inositol using allyl groups for ‘temporary’ protection. The benzyl ethers are required as intermediates for the synthesis of the ‘second messenger,’ inositol 1,4,5-trisphosphate and its metabolite, inositol 1,3,4-trisphosphate. 1,2,3,4-Tetra-O-benzyl-myo-inositol, and its two monoallyl and monoprop-1-enyl ethers, were also prepared as model compounds for phosphorylation studies of the vicinal 5,6-diol system which occurs in 1,2,4-tri-O-benzyl-myo-inositol.

Journal ArticleDOI
TL;DR: A dihydrocoumarin metabolite of Mammea africana has been prepared by Lewis acid-mediated acylation of 5,7-dihydroxy-4-pentyl-3,4-Dihydrocoupmarin (available by hydrogenation of the corresponding coumarin).
Abstract: A dihydrocoumarin metabolite of Mammea africana has been prepared by Lewis acid-mediated acylation of 5,7-dihydroxy-4-pentyl-3,4-dihydrocoumarin (available by hydrogenation of the corresponding coumarin). Acylation of 4-(1-methylpropyl)- and 4-(1-acetoxypropyl)-5,7-dihydroxycoumarin, each prepared by Pechmann condensation of phloroglucinol with the appropriate β-keto ester, gave 8-acylcoumarins that have been C-alkylated with 3-methylbut-2-enyl bromide to provide, respectively, mammea D/BB (ferruol A), and the natural insecticidal 4-(1-acetoxypropyl)coumarins of M.americana, mammea E/BA and E/BB; C-alkylation with 3,7-dimethylocta-2,6-dienyl chloride of 4-(1-acetoxypropyl)-5,7-dihydroxy-8-(2-methylbutyryl) coumarin afforded surangin B, an insecticidal component of M.longifolia.

Journal ArticleDOI
TL;DR: The role of bulk solvent on the energetics of non-dissociative proton transfer by intramolecular and tautomeric interconversion within a self-associated dimer was investigated in this article.
Abstract: The lactim–lactam tautomerism of 2-pyridone via non-dissociative proton-transfer mechanisms has been investigated using ab initio MO methods. Stationary points (minima and saddle points) on the potential energy surfaces for proton transfer by three classes of such mechanisms have been obtained: (i) an intramolecular mechanism, (ii) tautomeric interconversion within a self-associated dimer, and (iii) a mechanism involving one or two water molecules as a bifunctional catalyst. The latter two mechanisms were found to be more energetically favourable than the first. The role of bulk solvent on the energetics of proton transfer by these mechanisms has been investigated.

Journal ArticleDOI
TL;DR: In this paper, 1,4-Di-O-allyl-myo-inositol was converted into 1, 4-di-Oallyl -5,6-OISOPropylidene-myoinositol on kinetic acetonation.
Abstract: Racemic 1,2-O-isopropylidene-myo-inositol was converted into a mixture of 1,2 : 5,6-, 1,2 : 3,4-, and 1,2 : 4,5-di-O-isopropylidene-myo-inositols which were resolved by g.l.c. The 1,2 : 4,5- and 1,2 : 5,6- isomers were isolated from the mixture as benzoate derivatives. Allylation of the mixed isomers allowed the separation of all three allyl ethers by column chromatography and these were converted into the corresponding di-O-allyl-myo-inositols. 1,4-Di-O-allyl-myo-inositol was converted into 1,4-di-O-allyl-5,6-O-isopropylidene-myo-inositol on kinetic acetonation. Removal of the allyl groups from 5,6-di-O-allyl-1,2 : 3,4-di-O-isopropylidene-myo-inositol gave pure 1,2 : 3,4-di-O-isopropylidene-myoinositol which gave the known 1,2,3,4-tetra-O-benzyl-myo-inositol. Crystals of the diacetate of 1,2,5,6 tetra-O-benzyl-myo-inositol showed interesting ‘jumping’ behaviour on heating and cooling.

Journal ArticleDOI
TL;DR: The structure of the two factors of the novel glycopeptide antibiotic A40926 have been determined using a combination of FAB-MS, GC-MS and 1H n.r.m. studies.
Abstract: The structure of the two factors of the novel glycopeptide antibiotic A40926 have been determined using a combination of FAB-MS, GC-MS and 1H n.m.r. studies. A40926 Is a member of the vancomycin family of antibiotics and is structurally related to teicoplanin, A35512B and aridicin.

Journal ArticleDOI
TL;DR: In this article, the rate constant ket of electron transfer from cis-dialkylcobalt(III) complexes, cis-[R2Co(bpy)2]+(R = Me, Et, and PhCH2; bpy = 2,2′-bipyridine) to a series of p-benzoquinone derivatives (Q) in aqueous solution (H2O-EtOH; 5 : 1 v/v) or acetonitrile (MeCN) and from ferrocene derivatives (Fc) to the same
Abstract: The kinetics of acid catalysis of electron-transfer reactions from cis-dialkylcobalt(III) complexes, cis-[R2Co(bpy)2]+(R = Me, Et, and PhCH2; bpy = 2,2′-bipyridine) to a series of p-benzoquinone derivatives (Q) in aqueous solution (H2O–EtOH; 5 : 1 v/v) or acetonitrile (MeCN) and from ferrocene derivatives (Fc) to the same series Q and of photoinduced electron-transfer reactions from [Ru(bpy)3]2+* to acetophenone derivatives in MeCN have been studied at various concentrations of HClO4 as a catalyst at 298 K. The rate constant ket of electron transfer from cis-[Et2Co(bpy)]+ to Q in aqueous solution is independent of pH in the high pH region, pH > pK1 where K1 is the acid dissociation constant of the semiquinone radicals QH˙; the log ket value increases linearly with decreasing pH with slope of –1 in the region pK1 > pH > pK2 where K2 is the acid dissociation constant of hydroquinone radical cation QH2+˙. The slope changes to –2 in more acidic media, pK2 > pH. This dependence of log ket on pH in aqueous solution has been analysed quantitatively, based on the positive shift of the one-electron reduction potentials of Q in the presence of HClO4; the shift is caused by protonation of reduced species of Q. The positive shift of one-electron reduction potentials of carbonyl compounds (p-benzoquinone and acetophenone derivatives) in the presence of HClO4 has also been determined in MeCN by analysing the acid-catalysed electron-transfer reactions from cis-[Et2Co(bpy)2]+ and Fc to p-benzoquinone derivatives and the photoinduced electron-transfer reactions from [Ru(bpy)3]2+* to acetophenone derivatives in MeCN. The correlations between the redox and acid-base properties of carbonyl compounds and the factors determining the catalytic effect of acid on the electron-transfer reactions are discussed.

Journal ArticleDOI
TL;DR: The reaction of benzotriazole with an excess of aliphatic aldehydes and thionyl chloride in refluxing chloroform gives the corresponding 1-chloroalkanes as discussed by the authors.
Abstract: Reaction of benzotriazole with an excess of aliphatic aldehydes and thionyl chloride in refluxing chloroform gives the corresponding 1-(benzotriazol-1-yl)-1-chloroalkanes. Products with an α-hydrogen next to the chlorine-bearing carbon atom gradually eliminate hydrogen chloride with time or when heated. Nucleophilic displacements of the chlorine atom are described. Reaction of 2 mol equiv. of benzotriazole with 1 mol equiv. of aromatic or aliphatic aldehydes and an excess of thionyl chloride yields the corresponding bis(benzotriazol-1-yl)methylarenes and 1,1-bis(benzotriazol-1-yl)alkanes respectively; usually some of the corresponding 1-(benzotriazol-1-yl)-1-(benzotriazol-2-yl)alkanes are also formed. The 1-(benzotriazol-1-yl)-1-chloro-1-arylmethanes spontaneously react further to give bisbenzotriazolyl compounds.