Showing papers in "Journal of The Chemical Society-perkin Transactions 1 in 1980"
TL;DR: In this article, isolated primary and secondary hydroxy-groups in carbohydrate derivatives are transformed into iodo-groups with inversion of configuration on treatment with either triphenylphosphine, iodine, and imidazole or triphensyl-phosphines and 2,4,5-tri-iodoimidazoles at elevated temperatures.
Abstract: Isolated primary and secondary hydroxy-groups in carbohydrate derivatives are transformed into iodo-groups with inversion of configuration on treatment with either triphenylphosphine, iodine, and imidazole or triphenyl-phosphine and 2,4,5-tri-iodoimidazole at elevated temperatures. At lower temperatures, primary hydroxy-groups may be selectively replaced by iodo-groups.
317 citations
TL;DR: In this article, a C(4)-C(8)-or C(6)-linked polyflavan-3-ol structure was used to isolate polymeric proanthocyanidins from 22 plant sources.
Abstract: Homogeneous polymeric proanthocyanidins have been isolated from 22 plant sources and all are based on a C(4)–C(8)[or C(6)] linked polyflavan-3-ol structure. 13C N.m.r, spectroscopy in 2[H6]acetone–water is used to calculate the ratio of procyanidin to prodelphinidin monomer units, the average heterocyclic ring stereochemistry of the monomers, and the ratio of monomers to chain-terminating units. The majority of polymers isolated in this study possess monomers with predominantly a 2,3-cis stereochemistry [the same configuration as (–)-epicatechin]. The number-average molecular weight, calculated from monomer to terminal unit ratios, of the polymers is 1 500–5 000. The structure of the chain-terminating group is established by thiolysis degradation and g.l.c. analysis of the products.
256 citations
TL;DR: In this paper, the treatment of phenols with 2 mol equiv. of paraformaldehyde in aprotic and poorly electron-donating solvents in the presence of selected metal halides coupled with suitable bases is described.
Abstract: Treatment of phenols (1) with 2 mol equiv. of paraformaldehyde in aprotic and poorly electron-donating solvents in the presence of selected metal halides coupled with suitable bases produces salicylaldehydes (3) in high yields. The route is highly selective for ortho-formylation and also specific towards monoformylation. The crucial role of added bases is emphasized.
160 citations
TL;DR: The primary processes in the OH· radical-induced oxidation mechanism of sulphoxides have been investigated by pulse radiolysis and, in particular, by an improved conductivity detection method with a time resolution of ca. 50 ns in aqueous solution.
Abstract: The primary processes in the OH· radical-induced oxidation mechanism of sulphoxides have been investigated by pulse radiolysis and, in particular, by an improved conductivity detection method with a time resolution of ca. 50 ns in aqueous solution. Electrophilic addition of the OH· radical to the sulphoxide group leads to a transient adduct, R2SO(OH)· which decays unimolecularly with t1/2 up to 100 ns into a sulphinic acid, RSO2H, and a radical R·. The various RSO2H have been identified by their pKa, and R·(including t-butyl and phenyl radicals) by direct optical measurement or chemical scavenging experiments. The probability of radical split-off from R2SO(OH)· for mixed sulphoxides depends on the stability of the radical leaving. Depending on the nature of the sulphoxide substituents two other OH· radical reactions compete with, and may even predominate over, the addition at the sulphoxide group. Thus hydrogen-atom abstraction readily occurs from longer chain and branched aliphatic groups and in the presence of aromatic substituents OH· radicals add to the π-system to form a hydroxycyclohexadienyl radical. The respective yields, kinetics and some physico-chemical properties of the primary species are presented and discussed.
150 citations
TL;DR: The absolute rate constants of the one-electron transfer reactions of related aliphatic peroxyl radicals with ascorbate, promethazine, phenol, and tyrosine have been found to increase with increasing substitution of chlorine atoms.
Abstract: The peroxyl radicals Cl3COO·, Cl2CHOO·, ClCH2OO·, CH3OO; ·OOCCl2CO2–, ·OOCHClCO2–, ·OOCH2CO2–, ·OOCF2CO2–, and (CH3)2C(OH)CH2OO· have been generated in aqueous alcohol solutions by pulse radiolysis using the Brunel and Hahn-Meitner accelerators. The absolute rate constants of the one-electron transfer reactions of related aliphatic peroxyl radicals with ascorbate, promethazine, phenol, and tyrosine have been found to increase with increasing substitution of chlorine atoms. For the reaction of the radical Cl3CO2· and promethazine, at pH 6, k 6.0 ± 0.4 × 108 l mol–1 s–1 has been measured. For the analogous reaction of the radical ClCH2O2·, k 3.3 ± 0.2 × 107 l mol–1 S–1 has been determined.
101 citations
TL;DR: In this paper, the White-Bovill alkane-alkene force field (WBFF) has been modified and extended for the calculation of geometrical and thermodynamic properties of saturated compounds containing the isolated ether or the 1,4-dioxa grouping.
Abstract: The White–Bovill alkane–alkene force field (WBFF) has been slightly modified and extended for the calculation of geometrical and thermodynamic properties of saturated compounds containing the isolated ether or the 1,4-dioxa grouping. The new force field reproduces the heats of formation of 14 ethers with a mean deviation of 0.86 kcal mol–1 between observed and calculated enthalpies. Bond lengths, bond angles, and torsion angles are satisfactorily reproduced with mean deviations of 0.010 A, 1.0°, and 4.3° respectively over a set of 103 observations. The force field has been used to investigate the detailed relationship between the strain energies and the corresponding equilibrium geometries of various conformations of 9-crown-3, 12-crown-4, and 18-crown-6. The determination of the structure of the complex of 18-crown-6 with benzylammonium thiocyanate, by X-ray crystallography, is described and molecular mechanics calculations are used to comment upon the conformations adopted by 18-crown-6 in a range of complexes.
78 citations
TL;DR: The α form of quinol crystallises in the rhombohedral space group R with 54 molecules in each unit cell of hexagonal dimensions a=b= 38.46(2), c= 5.650(3)A, i.e. three times larger than the cell originally described by Caspari as mentioned in this paper.
Abstract: The α form of quinol crystallises in the rhombohedral space group R with 54 molecules in each unit cell of hexagonal dimensions a=b= 38.46(2), c= 5.650(3)A, i.e. three times larger than the cell originally described by Caspari. There are therefore 3 molecules in each asymmetric unit. Two of these are involved in forming two interpenetrating, open, hydrogen-bonded cageworks similar to those found in the structure of β-quinol and capable of clathrating small molecules such as CO2, N2, and Ar, whereas the third forms double helices consisting of hydrogen-bonded chains of quinol molecules round three-fold screw axes. The cageworks and helices are hydrogen-bonded together in such a way that the interpenetrating cageworks are connected (unlike the β structure) and the two strands of the double helix are connected. The overall α structure is more dense than the β structure and is the stable form at room temperature.
78 citations
TL;DR: The 3-acylpyrrolidine-2,4-diones (tetramic acids) can exist in solution as pairs of internal tautomers and as a pair of external tautomer as mentioned in this paper.
Abstract: The 3-acylpyrrolidine-2,4-diones (tetramic acids) can exist in solution as pairs of internal tautomers and as a pair of external tautomers. The tautomer constitution of a number of bioactive 3-acylpyrrolidine-2,4-diones, e.g. α-cyclopiazonic acid (1) and tenuazonic acid (3), has been studied. The study was facilitated by 1H and 13C n.m.r. spectroscopy and single crystal X-ray crystallography. From these results the structures of a number of natural products containing the 3-acylpyrrolidine-2,4-dione unit have been revised.
78 citations
TL;DR: The plant enzyme was studied by administration of (αS)-[α-3H,U-14C]tyrosine to intact Papaver somniferum plants followed by isolation of the resultant papaverine, which retained no tritium; morphine was also isolated to act as an internal standard.
Abstract: Tyrosine is proved to be decarboxylated with retention of configuration by three aromatic amino-acid decarboxylases of bacterial, mammalian, and plant origin by experiments based on the synthesis of (αS)-[α-3H]tyrosine and the (αR)- and (αS)-isomers of [α-3H1]tyramine. Incubation of the labelled tyramines with the diamine oxidase from pea seedlings and the monoamine oxidase from rat liver shows that the former enzyme removes Hsi and the latter HRe. These amine oxidases are used to assay the chirality of the [α-3H1]tyramines produced by incubation of suitably labelled tyrosines in tritiated water or in unlabelled water with the partially purified decarboxylases from Streptococcus faecalis and hog kidney. The plant enzyme was studied by administration of (αS)-[α-3H,U-14C]tyrosine to intact Papaver somniferum plants followed by isolation of the resultant papaverine, which retained no tritium; morphine was also isolated to act as an internal standard.
76 citations
TL;DR: The addition of aromatic amines to terminal acetylenes in the presence of catalytic amounts of mercury(II) chloride gives imines, enamines, and 1,2,3,4-tetrahydroquinoline derivatives as discussed by the authors.
Abstract: The addition of aromatic amines to terminal acetylenes in the presence of catalytic amounts of mercury(II) chloride gives imines, enamines, and 1,2,3,4-tetrahydroquinoline derivatives; mercury(II) acetate shows considerably less catalytic activity and may be used for the non-catalytic preparation of imines, enamines, NN′-disubstituted acetamidines, and NN-disubstituted acetamides.
74 citations
TL;DR: In this article, triphenylphosphine-carbon tetrabromide-lithium azide was used for azidation of unprotected or appropriately protected nucleosides.
Abstract: Regioselective azidation of unprotected or appropriately protected nucleosides was conducted by means of the reagent triphenylphosphine–carbon tetrabromide–lithium azide. By use of this reagent, 5′-azido-5′-deoxynucleosides were prepared conveniently in one step from nucleosides in high yields. Secondary hydroxy-groups of appropriately 5′-protected nucleosides were also converted by the reagent to azido-functions with complete inversion.
TL;DR: The electrophilic substitution reaction of indole with acetone in the presence of boron trifluoride has been followed and the structures of two of the three products isolated have been established as mentioned in this paper.
Abstract: The electrophilic substitution reaction of indole with acetone in the presence of boron trifluoride has been followed and the structures of two of the three products isolated have been established. The structure of compound (1), dimer II, was determined by X-ray diffraction methods as crystals from methanol were monoclinic, space group Cc, and had cell parameters a= 13.383(2), b= 14.064(2), c= 11.638(4)A, β= 114.74(2)°, Z= 4. The structure was refined to a final R value of 0.068.
TL;DR: In this paper, the reductive elimination of vicinal benzoyloxy-sulphones gives products with a trans : cis ratio of ca. 4 : 1, where the original Z-geometry is preserved in the product; (Z)-2-methylbut-2-enyl p-tolyl sulphone and tiglic aldehyde give almost exclusively (2E,4E,6Z)-3,6-dimethylocta-2,4, 6-triene (27).
Abstract: When applied to the construction of internal disubstituted double bonds in compounds such as pentadec-7-ene and 2,6,11,15-tetramethylhexadeca-2,6,8,10,14-pentaene (5), the reductive elimination of vicinal benzoyloxy-sulphones gives products with a trans : cis ratio of ca. 4 : 1. When applied to the construction of disubstituted olefins in which branching occurs adjacent to the newly formed double bond, much higher trans-stereoselectivity is observed, e.g, for 5-ethyl-2-methylhept-3-ene (21) and 3,6-dimethylocta-2,4,6-triene (25) it is at least 98%. A similar effect of chain-branching is also observed in some Wittig and Homer reactions using primary allylic phosphorus derivatives. When a Z-allylic sulphone is used as the starting material in the benzoyloxy-sulphone method, the original Z-geometry is preserved in the product; (Z)-2-methylbut-2-enyl p-tolyl sulphone and tiglic aldehyde give almost exclusively (2E,4E,6Z)-3,6-dimethylocta-2,4,6-triene (27).
TL;DR: The trifluoromethyl iodide and copper powder in hexamethylphosphoric triamide and filtering off the excess of copper powder was used to synthesize the following nucleosides.
Abstract: Halogenated nucleoside derivatives were trifluoromethylated using a solution of a trifluoromethyl–copper complex, which was prepared by shaking trifluoromethyl iodide and copper powder in hexamethylphosphoric triamide and filtering off the excess of copper powder The following trifluoromethylated nucleosides were obtained in moderate to good yields: 5-trifluoromethyl-uridine, -deoxyuridine, -cytidine, -deoxycytidine, and -arabinosylcytosine; 8-trifluoromethyl-adenosine, -deoxyadenosine, and -inosine; and 6-trifluoromethylribofuranosylpurine This procedure offers simple synthesis of many trifluoromethyl compounds
TL;DR: In this article, the conformational enthalpy differences and conformational entropy differences for methyl, ethyl, and isopropyl groups in alkylcyclohexanes were investigated at low temperatures of solutions in CFCl3-CDCl3.
Abstract: 13 C N.m.r. studies at low temperatures of solutions in CFCl3–CDCl3 of [Me-13C]methylcyclohexane, [α-13C]-isopropylcyclohexane, cis-1-ethyl-4-methylcyclohexane, cis-1-isopropyl-4-methylcyclohexane, and cis-1-ethyl-4-isopropylcyclohexane have yielded conformational enthalpy differences and conformational entropy differences for methyl, ethyl, and isopropyl groups in alkylcyclohexanes. For –ΔH°, the averaged values obtained, in kcal mol–1, were 1.75 (Me), 1.60 (Et), and 1.52 (Pri); for ΔS°, the averaged values, in cal mol–1 K–1, were –0.03 (Me), 0.64 (Et), and 2.31 (Pri). The determined values are in good agreement with those calculated by the Allinger group for the gas phase, using a method based on classical mechanics. As a result of the opposing trends for –ΔH° and ΔS° values, the sequence of –ΔG° values at 300 K, namely Pri > Et > Me, is reversed at temperatures below ca. 40 K.
TL;DR: In this paper, a 1 : 1 complex is formed between the metal ion and penicillin which is attacked by hydroxide ion up to 108 fold faster than the uncoordinated compound.
Abstract: The metal(II)-ion catalysed hydrolysis of some pencillin and cephalosporin derivatives in water at 30° shows saturation kinetics. A 1 : 1 complex is formed between the metal ion and penicillin which is attacked by hydroxide ion up to 108 fold faster than the unco-ordinated compound. The site of co-ordination of the penicillins and copper(II) ions is the β-lactam nitrogen and the carboxylate group. The association constants for the cephalosporins and metal ions are greater than those for the penicillins but the transition states for the cephalosporin reaction with hydroxide ion bind less tightly to metal ions. The order of rate enhancement brought about by the metal ion is CuII > ZnII > NiII∼ CoII. The metal ions are thought to stabilise the tetrahedral intermediate formed by hydroxide ion attack on the β-lactam. Some comments are made about metal ions as electrophilic catalysts in enzymes.
TL;DR: It is shown that histidine decarboxylase acts on histamine to bring about slow exchange with the medium of the α-Re-hydrogen, which occupies the same space (Re-space) as the carboxy-group of (αS)-histidine.
Abstract: (αS)-[α-3H]Histidine is prepared and the [α-3H1]histamine produced from it by the decarboxylating enzymes of Clostridium welchii and Lactobacillus 30a is proved by assay with diamine oxidase from pea seedlings to have the (αS)-configuration. The (Si)-stereospecificity of the latter enzyme is confirmed for the case of histamine by studying its action on (αR)-[α-3H1]histamine (21) which is synthesised rationally. The combined results prove that histidine decarboxylases from both sources bring about decarboxylation with overall retention of configuration. It is shown that histidine decarboxylase acts on histamine to bring about slow exchange with the medium of the α-Re-hydrogen, which occupies the same space (Re-space) as the carboxy-group of (αS)-histidine. Syntheses are described of (αS,βS)-[β-3H1]histidine (45) and (αS,βR)-[β-3H1]histidine (47).
TL;DR: A one-step biomimetic synthesis in high yield of the natural flavanolignans silybin and isosilybin from 2R,3R-dihydroquercetin and coniferyl alcohol is reported.
Abstract: Oxidative coupling of substituted catechols with isoeugenol or coniferyl alcohol in the presence of silver oxide affords 2,3-trans-1,4-benzodioxans in good yield. The reaction is highly regioselective when the catechol bears an alkyl substituent, much less so in the case of an electrophilic one. A free-radical coupling mechanism is proposed. A one-step biomimetic synthesis in high yield of the natural flavanolignans silybin and isosilybin from 2R,3R-dihydroquercetin and coniferyl alcohol is reported.
TL;DR: Bisdethiobis(methylthio)gliotoxin was identified as an amorphous, minor metabolite of Gliocladium deliquescens and characterised via the crystalline bis-4-bromobenzoate of the corresponding didehydro-derivative.
Abstract: Bisdethiobis(methylthio)gliotoxin (2) has been identified as an amorphous, minor metabolite of Gliocladium deliquescens and characterised via the crystalline bis-4-bromobenzoate of the corresponding didehydro-derivative. The new metabolite has been synthesised from gliotoxin (1) by reduction and methylation. Feeding experiments with [14C]-(1) and -(2), prepared biosynthetically from L-[U-14C]phenylalanine, have shown that bisdethiobis(methylthio)gliotoxin is formed (8.6% incorporation), apparently irreversibly, from gliotoxin in G. deliquescens.
TL;DR: The kinetic parameters for β-fission of radicals containing the cyclobutylcarbinyl system have been determined by analysis of the mixtures obtained when suitable chloro-compounds are treated with tributylstannane as mentioned in this paper.
Abstract: The kinetic parameters for β-fission of radicals containing the cyclobutylcarbinyl system have been determined by analysis of the mixtures obtained when suitable chloro-compounds are treated with tributylstannane. Under these conditions ring opening is irreversible and in the rigid bicyclic system (4) is under stereoelectronic control. For ring opening of cyclobutylcarbinyl radical (8)kf= 4.3 × 103 s–1 at 60°, and the best values of the activation parameters appear to be ΔH‡= 12.2 kcal mol–1 and ΔS‡=–7.4 cal mol–1 K1. Monocyclic systems undergo preferential fission of the more substituted βγ-bond. Methyl substituents at the α-, β-, or δ-positions have little effect but γ-substitution strongly enhances the rate of ring opening. The transition state is reactant-like and has a similar disposition of centres to that (1) for homolytic addition.
TL;DR: In this paper, an equilibrium was found between (R2S)2+˙ radical anions, X2−˙ anions and R2S∴X radical cations in the presence of halide ions.
Abstract: In the presence of halide ions, stabilization of oxidized sulphur centres in organic sulphides can occur via formation of three electron S∴X bonds to yield R2S∴X radicals. An equilibrium is found to exist between these species, X2–˙ radical anions, and (R2S)2+˙ radical cations. Equilibrium constants for the processes X2–˙+ R2S ⇌ R2S∴X + X–, R2S∴X + R2S ⇌(R2S)2+˙+ X–, R2S∴X ⇌ R2S+˙+ X–, and R2S∴X ⇌ R2S + X˙ have been determined, together with the optical properties of R2S∴X, where R = Me and Et, and X = Cl, Br, and I. The absolute stability of the S∴X bond increases as the difference in electronegativity between S and X decreases and is thus highest for R2S∴I. In addition, rate constants for formation and decay processes of R2S∴X are reported.
TL;DR: Tertiary phosphine-palladium complexes catalyse the co-oligomerization reaction of butadiene and carbon dioxide under mild conditions of temperature and pressure (70 °C, 100 atm) to yield (E)-2-ethylidenehept-6-en-5-olide (2) and octadienyl esters of 2-vinylhepta-4,6-dienoic acid (4b, c).
Abstract: Tertiary phosphine–palladium complexes catalyse the co-oligomerization reaction of butadiene and carbon dioxide under mild conditions of temperature and pressure (70 °C, 100 atm) to yield (E)-2-ethylidenehept-6-en-5-olide (2) and octadienyl esters of (E)-2-ethylidenehepta-4,6-dienoic acid (3b, c) and of 2-vinylhepta-4,6-dienoic acid (4b, c). At higher temperature (90 °C) esters (3b, c) yield octa-1,3,7-triene and (E)-2-ethylidenehepta-4,6-dienoic acid through an oxidative addition of the allyl carbon–oxygen bond to a palladium(0) species. Subsequent reactions of the carboxylic acid in the presence of [PdLn](L = tertiary phosphine) complexes yield (E)-2-ethylidenehept-5-en-4-olide (1) and 2-ethylhepta-2,4-dien-4-olide (5).
TL;DR: Quinoline and 6- or 8-substitutedquinolines were hydrogenated catalytically on platinum under either weakly basic (solvent McOH) or strongly acidic (solent CF3CO2H) conditions as mentioned in this paper.
Abstract: Quinoline (1) and the 6- or 8-substituted-quinolines (2)–(14)(R = Me, Pri, But, Ph, OMe, OH, CF3, or F) were hydrogenated catalytically on platinum under either weakly basic (solvent McOH) or strongly acidic (solvent CF3CO2H) conditions. In methanol the only product was the corresponding 1,2,3,4-tetrahydro-compound. In trifluoroacetic acid, compounds hydrogenated in the benzene ring were isolated as major products; both electronwithdrawing and electron-donating substituents at C-6 or C-8 cause (sometimes drastic) reduction in yield. The products were characterized by their 1H and 13C n.m.r. spectra.
TL;DR: In this paper, the reduction of a compound with isocyanide and xanthate functions in a 1,2-relationship gives a smooth radical fragmentation to furnish an olefin.
Abstract: Primary, secondary, and tertiary aliphatic or alicyclic isocyanides are smoothly reduced under radical conditions using tri-n-butylstannane to the corresponding hydrocarbons. The relative ease of reduction is tertiary > secondary > primary. Aromatic isocyanides are not reduced under these conditions. The reduction of isothiocyanates (or isoselenocyanates) by tri-n-butylstannane also affords hydrocarbons, but here the isocyanides have been shown to be intermediates. The reduction of a compound with isocyanide and xanthate functions in a 1,2-relationship gives a smooth radical fragmentation to furnish an olefin. An efficient synthesis of 2-deoxy-D-glucose starting with glucosamine is described.
TL;DR: The specific rate of O → N acyl group migration is pH independent and shows a low solvent effect (m 0175) Substituents attached to carbon or nitrogen have the same effect (ρ−084) when the migrating group R is varied a non-linear Hammett plot is observed, with ρ+060 for electron-withdrawing and +165 for electrondonating substituents.
Abstract: When imidoyl chlorides (8) are solvolysed in the pH range 3–13 in aqueous dioxan in the presence of acetate or benzoate ions, the isoimides (10) are formed in situ These isoimides undergo acid (pH 115) catalysed acyl transfer to the solvent, giving the amides (12) But at intermediate pH (6–11) rearrangement to the N-acyl form (11)(the Mumm rearrangement) alone occurs The specific rate of this O → N acyl group migration is pH independent and shows a low solvent effect (m 0175) Substituents attached to carbon or nitrogen have the same effect (ρ–084) When the migrating group R is varied a non-linear Hammett plot is observed, with ρ+060 for electron-withdrawing and +165 for electron-donating substituents The changeover point is a function of the migrating terminus varying from R = Ph (when Y = H) to R =p-tolyl (when Y =p-NO2) Rate-determining O → N acyl transfer is suggested in all cases, but this is preceded by an equilibrium which favours the Z form (10a) when R is electron donating
TL;DR: Condensation of 2-chloro- and 2-3-dichloro-quinoxalines with alk-1-ynes in the presence of bis(triphenylphosphine)palladium(II) dichloride and copper(I) iodide gives mono- and di-alkynylquinoxalinine derivatives as discussed by the authors.
Abstract: Condensation of 2-chloro- and 2,3-dichloro-quinoxalines with alk-1-ynes in the presence of bis(triphenylphosphine)palladium(II) dichloride and copper(I) iodide gives mono- and di-alkynylquinoxalines. Addition of amines to these products gives stable enamines; hydration gives 2′-oxoalkyl compounds which exist predominantly in the intramolecularly hydrogen-bonded enol form. Condensation of the alkynylquinoxalines with diethyl sodiomalonate, and related compounds, yields pyrido[1,2-a]quinoxalin-4-one derivatives. 2-Alkynyl-3-chloro quinoxalines are intermediates for convenient syntheses of pyrrolo[2,3-b]quinoxalines.
TL;DR: In this paper, it was shown that 3-bromobenzofuran with trifluoromethyl iodide and copper powder in pyridine gave 2,3-bis(trifluorsomethymyl)-benzofuran.
Abstract: Reaction of 3-bromobenzofuran with trifluoromethyl iodide and copper powder in pyridine gave 2-(trifluoromethyl)-, 2- and 3-(pentafluoroethyl)-, and 2,3-bis(trifluoromethyl)-benzofuran, as well as the expected product, 3-(trifluoromethyl)benzofuran. Bromoanisole also gave (trifluoromethyl)anisole and (pentafluoroethyl)anisole, but introduction of the perfluoroalkyl group occurred at the position originally occupied by the bromine. Formation of pentafluoroethyl compounds is explained by decomposition of trifluoromethylcopper to cuprous fluoride and difluorocarbene, which can then react with a further molecule of trifluoromethylcopper to form pentafluoroethylcopper. This then reacts with aryl halide to give pentafluoroethyl compounds. Perfluoroalkylcopper is thermally cleaved to perfluoroalkyl radical, which then reacts with pyridine to give perfluoroalkylpyridines. This mechanism must be involved in the formation of 2,3-bis(trifluoromethyl)benzofuran. Introduction of a perfluoroalkyl group to the position originally unoccupied with halogen might be due to the rather localized double bond in benzofuran.
TL;DR: In this paper, a neutralization reaction on the macroreticular anion-exchange resin Amberlyst A-26 was used for the sequential hydrolysis and olefination of dioxolans.
Abstract: Phosphonates substituted with electron-withdrawing groups (CN and CO2Me) have been supported, by means of a neutralization reaction, on the macroreticular anion-exchange resin Amberlyst A-26. Treatment of carbonyl compounds with the polymer-bound phosphonate in various solvents gave olefins in high yields, at room temperature. Either batch or column techniques are employed, the latter offering the opportunity of a continuous procedure. The simultaneous use of the phosphonate resin and of an acidic one (Amberlyst 15 H) allowed the direct sequential hydrolysis and olefination of dioxolans.
TL;DR: In this paper, the isolation and structure of four new pigments, nigerone (la), 6′-O-demethylnigerone(1b), isonigerone and heminigerone, are described.
Abstract: The isolation and structure of four new pigments, nigerone (la), 6′-O-demethylnigerone (1b), isonigerone (2), and heminigerone (3), are described. A study of the chiroptical properties of the dimers indicates the S-configuration.
TL;DR: In this paper, the synthesis of methyl 2,4-dihydroxy-6-methyl-(1a) and -3,6-dimethylbenzoates (1b) were described.
Abstract: Syntheses of methyl 2,4-dihydroxy-6-methyl-(1a) and -3,6-dimethylbenzoates (1b) and methyl 2,4-dihydroxy-6-pentylbenzoate (1c) are described. Condensation reactions of dimethyl sodiomalonate with the dianion derived from pentane-2,4-dione or the dimerisation of the methyl acetoacetate dianion or the acetylation of the trianion derived from methyl 3,5,7-trioxo-octanoate gave (1a)(⩽78%) after work-up at pH 9. Analogous convenient, short, optimised syntheses of (1b and c) are given in detail.