Synthesis of biologically active phosphorus heterocycles via cyclization reactions of Lawesson's reagent

2,4‐Bis(4‐methoxyphenyl)‐1,3,2,4‐dithiaphosphetane‐2,4‐disulfide (Lawesson's reagent, LR) reacted with certain bifunctional compounds, such as glycinamides 1, 1‐glyceryl monoesters 4, and 3‐mercapto‐4‐amino‐5‐substituted‐1,2,4‐triazoles 6, to yield five‐membered phosphorus heterocycles 3,5, and 7, respectively. The cycloaddition reaction of LR with 1,3‐butadiene 8 was investigated to form the six‐membered heterocycle 9. The results of preliminary bioassays showed that these heterocycles obtained via cyclization reactions of LR possess significant selective herbicidal activity. The QSAR of 3 was also made. In conclusion, the cyclization reactions of LR with bifunctional substrates and 1,3‐dienes afford novel routes to the syntheses of biologically active phosphorus heterocycles. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 105–111, 1999     

Determination of chlorophenoxy acid herbicides and their esters in soil by capillary high performance liquid chromatography with ultraviolet detection, using large volume injection and temperature gradient

A simple method for the simultaneous determination of chlorophenoxy acid herbicides and their esters in soil is presented. Compounds studied are: 2,4-dichlorophenoxyacetic acid (2,4-D), 4-(2,4-dichlorophenoxy)butanoic acid (2,4-DB), 2,4-dichlorophenoxyacetic-1-butyl ester (2,4-D-1-butyl ester), and 2,4-dichlorophenoxyacetic-1-methyl ester (2,4-D-1-methyl ester).

The chromatographic analysis was carried out by HPLC, after ultrasonic extraction, on a C₁₈ packed capillary column with temperature gradient, large injection volumes and UV detection at 232 nm. Samples were spiked with amounts between 2.5 and 6.0 μg g⁻¹ of each herbicide; recoveries obtained were between 72 and 97% (n=3 for each spiked level) and detection limits were between 0.3 and 0.5 μg g⁻¹.

Application of this procedure to the analysis of herbicides in ester and acid forms showed the effectiveness of the methodology proposed.     

Synthesis of Phosphorus Derivatives of Pyrazolo[3,4-d]pyrimidine

Pyrazolo[3.4-d]pyrimidines are of considerable chemical and pharmacological importance as purine analogs^[1]. Various related compounds of these also show anti-tumor, anti-leukemic and antiviral activities^[2,3]. In addition,α-aminoalkylphosphonic acid are well known for their wide range of biological activities. They serve in agrochemistry as antifungal agents, herbicides and plant regulators^[4]. Recently, it was discovered that some derivatives of α-aminoalkylphosphonic acid also exhibit good antiphytoviral activity^[5]. As an extension of our studies on plant virucides, we now wish to report the synthesis of some novel phosphorus derivatives of pyrazolo[3,4-d]pyrimidine-6-ones 4,which may have antiviral activity.     

Synthesis of 6-(1-Aryl-5-methyl-1,2,3-triazol-4-yl)-3-(4-Pyridyl)-s-Triazolo[3,4-b]-l,3,4-Thiadiazoles

A survey of literature¹ revealed that s-triazolo[3,4-b]-1,3,4-thiadiazole, an interesting fused system of s-triazole and 1,3,4-thiadiazole rings, has received much attention during recent years on account of its prominent utilizations as antifungal, antiinflammatory, antiviral, analgesic and anthelmintic agents probably resulting from its planner and compact structure. Our earlier work on the synthesis of this class of heterocycles showed antibacterial, herbicidal and plant growth regulative properties^2-3 for the compounds. 1,2,3-Triazole derivatives have found their wide use in medicine, agriculture and industry^4-5. Incorporation of 1,2,3-triazole moiety into the 6-position of this ring system may lead to achieving compounds of better biological activities. In view of the above findings coupled with scanty reports on these condensed compounds carrying 6-heterocyclic groups, we wish to report here the condensation of 4-amino-5-mercapto-3-(4-pyridyl)-l,2,4-triazole(2) with 1-aryl-4-carboxy-5-methyl-1,2,3-triazoles(1_a-j) as a part of our continuing interest in this area.     

The reaction of cis dioxobis(2,4 pentanedionato)molybdenum (VI) and 2,2′ pyridylbenzoxazole (L), a novel route to β[Mo8O26]

MoO₂(C₅H₇O₂)₂, where C₅H₇O₂ is 2,4-pentanedione (acac), reacts with 2-2′ pyridylbenzoxazole in acetone to give a product with stoichiometry, Mo₃C₂₄H₁₆N₆O₁₂. This product dissolves readily in dimethylformamide to give a brown solution which on standing for several weeks yielded crystals. An X-ray structure determination showed these crystals to contain uncoordinated 2-2′pyridylbenzoxazole and [(CH₃)₂NH₂]₄⁺[Mo₈O₂₆]⁴⁻.     

Syntheses of 3-[5-Methyl-1-(4-Methylphenyl)-1,2,3-Triazol-4-yl]-6-Substituted-s-Triazolo[3,4-b]-1,3,4-Thiadiazoles

1,2,3-Triazole derivatives have been reported as inhibiting tumor proliferation, invasion, and metastasis^[1]. The fused l,3,4-triazolo[3,4-b]-1,3,4-thiadiazoles derivatives show various biological effects such as antifungal^[2], antibacterial, hypotensive and CNS depressant activities^[3]. We have reported several 6-aryl-3-[5-methyl-1-(4-methylphenyl)-1,2,3-triazol-4-yl]-s-triazolo[3,4-b]-1,3,4-thiadiazoles in the previous paper^[4]. The novel 6-aryl-3-[5-methyl-1-(4-methylphenyl)-1,2,3-triazol-4-yl]-s-triazolo[2,4-b]-1,3,4-thiadiazoles 6a-j have been synthesized by the condensation of 4-amino-5-mercapto-3-[5-methyl-1-(4-methylphenyl)-1,2,3-triazol-4-yl]-s-triazole 5 with various aromatic carboxylic acids in the presence of phosphorus oxychloride. The mercaptotriazole 5 was prepared from 4,the latter being prepared from 1 throng 2 and 3. The title compounds 6 were depicted in scheme 1. The structures of these compounds were established by elemental analysis, NMR, MS and IR techniques.     

Synthesis of 6-aryl-3-cinchophenyl-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles

In recent years, fused heterocycles have been found to possess many unique properties in synthesis and pharmacology. Especially, 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles derivatives have been attracting much attention of chemists and pharmacologists because of their broad-spectrum biological activities such as antibacterial¹, hypotensive and CNS depressant² activities. We have prepared some 3,6-substituted 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles and found that these compounds exhibited antimacrobial, insecticidal and promote plant growth.^3-5 Cinchophen had been used widely as medicine in clinic,but has been obsolete in recent years due to its by-effect. In order to seek for other uses of cinchophen, as a continuation of our preceeding studies, we used cinchophen as the starting material to synthesize ten new 6-aryl-3-cinchophenyl-l,2,4-triazolo[3,4-b]-l,3,4-thiadiazoles 5a-j. Compound 1 was prepared by the reaction of cinchophen and ethanol in the presence of sulfuric acid. 1 then reacted with hydrazine hydrate in absolute ethanol to give 2 which yielded 3 on treatment with CS₂ and KOH. On refluxing of 3 with excess hydrazine hydrate, 4 was obtained. 4 reacted with various substituted benzoic acids in the presence of POCl₃ to afifort 5a-j.     

Inverse phase transfer catalysis. Kinetics of the pyridine 1-oxide-catalyzed reactions of dichlorobenzoyl chlorides and benzoate ions

The substitution reactions of 2,3-, 2,4-, 3,4-, or 3,5-dichlorobenzoyl chloride (Cl₂C₆H₃COCl) and 2,3-, 2,4-, 3,4-, or 3,5-dichlorobenzoate ion (Cl₂C₆H₅COO⁻) or benzoate ion (C₆H₅COO⁻) in a two-phase H₂O/CH₂Cl₂ medium using pyridine 1-oxide (PNO) as an inverse phase transfer catalyst were investigated. The reaction of Cl₂C₆H₃COCl and PNO in CH₂Cl₂ to produce the ionic intermediate, 1-(dichlorobenzoyloxy)-pyridinium chloride (Cl₂C₆H₃COONP⁺Cl⁻) is the rate-determining step. In the PNO-catalyzed two-phase reaction of Cl₂C₆H₃COCl and C₆H₅COONa, the order of reactivities of Cl₂C₆H₃COCl toward reaction with PNO is (2,3-, 2,4-)>3,5->3,4-2,6-Cl₂C₆H₃COCl, whereas it is 3,5->(2,3-, 3,4-)>2,4-Cl₂C₆H₃COCl in the PNO-catalyzed two-phase reaction of Cl₂C₆H₃COCl and the corresponding Cl₂C₆H₃COONa. The order of reactivities of Cl₂C₆H₃COO⁻ ions towards the reaction with 1-(benzoyloxy)-pyridinium (C₆H₅COONP⁺) ion is (3,4-, 3,5-)>(2,3-, 2,4-Cl₂C₆H₃COO⁻).     

Enzymatic biosensor for the electrochemical detection of 2,4-dinitrotoluene biodegradation derivatives

In this work, we demonstrate for the first time that 4-methyl-5-nitrocatechol (4M5NC) and 2,4,5-trihydroxytoluene (2,4,5-THT), two compounds obtained from the 2,4-DNT biodegradation are recognized by polyphenol oxidase as substrates. An amperometric biosensor is described for detecting these compounds and for evaluating the efficiency of the 2,4-DNT conversion into 4M5NC in the presence of bacteria able to produce the 2,4-DNT-biotransformation. The biosensor format involves the immobilization of polyphenol oxidase into a composite matrix made of glassy carbon microspheres and mineral oil. The biosensor demonstrated to be highly sensitive for the quantification of 4M5NC and 2,4,5-THT. The analytical parameters for 4M5NC are the following: sensitivity of (7.5 ± 0.1) × 10⁵ nAM⁻¹, linear range between 1.0 × 10⁻⁵ and 8.4 × 10⁻⁵ M, and detection limit of 4.7 × 10⁻⁶ M. The sensitivity for the determination of 2,4,5-THT is (6.2 ± 0.6) × 10⁶ nAM⁻¹, with a linear range between 1.0 × 10⁻⁶ and 5.8 × 10⁻⁶ M, and a detection limit of 2.0 × 10⁻⁷. Under the experimental conditions, it was possible to selectively quantify 4M5NC even in the presence of a large excess of 2,4-DNT. The suitability of the biosensor for detecting the efficiency of 2,4-DNT biotransformation into 4M5NC is demonstrated and compared with HPLC-spectrophotometric detection, with very good correlation. This biosensor holds great promise for decentralized environmental testing of 2,4-DNT.     

Palladium-Catalyzed Carbonylative Reaction of Iodine Heterocyclic Compound with Alcohol

In the past few decades, much attention has been focused on palladium-catalyzed carbonylative reactions^[1,2], which is a simple method to synthesize some complicated compounds^[3,4]. This kind of reactions, however, can be carried out only when the substrates are arylhalide, heteroaryl halide, alkene halide,aryltrifluoromethyl-sulfonate and hypervalent iodonium salt^[5] etc. Herein, we report a palladium-catalyzed carbonylative reaction between 3,7-bis(N,N-dimethylamino)-10H-dibenz[b,e] iodinium iodide(1)^[6] with alcohols (2) at ambient temperature as shown in scheme.     

Fluorine-containing 3-arylhydrazono-2,4-dioxobutanoates in reactions with difunctional nucleophiles

3-Arylhydrazono-4-polyfluoroalkyl-2,4-dioxobutanoates reacted with hydrazines to give ethyl 4-aryldiazeno-3-polyfluoroalkyl-1H-pyrazole-5-carboxylates, while analogous reactions of ethyl 3-arylhydrazono-4-pentafluorophenyl-2,4-dioxobutanoates resulted in the formation of 4-aryldiazeno-3-pentafluorophenyl-1,2-dihydropyridazine-5,6-diones or 6-aryl-7,8,9,10-tetrafluoro-2-phenyl-2,4a,6,10b-tetradropyridazo[4,3-c]cinnoline-3,4-diones, depending on the conditions. Cyclocondensation of ethyl 3-arylhydrazono-4-polyfluoroalkyl(or pentafluorophenyl)-2,4-dioxobutanoates with ethylenediamine led to 3-[1-arylhydrazono-2-oxo-2-polyfluoroalkyl(or pentafluorophenyl)ethyl]-5,6-dihydropyrazin-2(1H)-ones, and 3-[1-arylhydrazono-2-oxo-2-polyfluoroalkyl(pentafluorophenyl)ethyl]benzoxazin-2-ones were formed in the condensation with o-aminophenol. Pentafluorophenyl-substituted heterocycles were found to undergo intramolecular ring closure to give 3-hetaryl-substituted 1-aryl-5,6,7,8-tetrafluoro-1,4-dihydrocinnolin-4-ones. The reactions of ethyl 3-arylhydrazono-4-pentafluorophenyl-2,4-dioxobutanoates with o-aminobenzenethiol gave 3-[7-(2-aminophenylsulfanyl)-1-aryl-5,6,8-trifluoro-4-oxo-1,4-dihydrocinnolin-3-yl]benzothiazin-2-ones; 8a-hydroxy-11,12,13,14-tetrafluoro-10-(4-methoxyphenyl)-2,3,4,5,6,7,8a,10-octahydropyrazino[1′,2′:4,5][1,4]diazepino[6,7-c]cinnolin-8-one was isolated in the condensation of ethyl 3-(4-methoxyphenylhydrazono)-4-pentafluorophenyl-2,4-dioxobutanoate with N-(2-aminoethyl)ethane-1,2-diamine.     

Application of Lawesson'S Reagent in Syntheses of Biologically Active Phosphorus Heterocycles

Abstract

The reactions of Lawesson's reagent-2.4-Bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide, with long-chain 1 - glycerin rnonoethers, 3-mercapto-4-amino-1,2,4-triazoles, 1,3-disubstituents glycinamides, and 2-methyl-1,3-butadiene have been investigated and found to form cyclic analogues 1, fused heterocycles 2, 5-membered phosphorus rings 3, and 6-membered heterocycle 4, respectively, in moderate yield. The preliminary biological screening tests for these rings showed that they possess significant selective herbicidal activity against rape.     

Reaction of octafluorotoluene, 3,5-dichlorotrifluoropyridine, 3-chlorotetrafluoro-yridine and tetrafluoropyrimidine with alkali-metal oximates

Treatment of octafluorotoluene (2) with approximately one-molar equivalents of the oximates R¹R²C = NO~ M⁺ (R¹ = R²=Me;R¹ = R² = Ph; R¹ = Me, R² = Ph;M = Na) (6a-c) in diethyl ether gives 4-(R¹R²C = NO)C₆F₄CF₃ (7a-c) as the only isolated products. Corresponding reaction of 3,5-dichlorotrifluoropyridine (3) with the oximates 6a-c affords 4-and 2-(R¹R²C = NO)C5F₂C12N (8a-c) and (9a-c), respectively (4-/2ratios at −35 °C: 65:35; 30:70; 12:88) ; the lithium oximates (R¹ = R² =Ph ; R¹ = Me, R² = Ph; M = Li) (6d) and (6e) give comparable results. With 3-chlorotetrafluoropyridine (4), treatment with sodium oximate 6c gives 4-(PhCMe = NO)-3-ClC₅F₃N (10) and 2-(PhCMe = NO)-5ClC₅F₃N (11) (ratio 44:56 at −35 °C). Such competition between S_NAr attack of these alkali-metal oximates at the C-4 and C-2 positions of chlorofluoropyridines 3 and 4 can be rationalized by invoking chelation of an alkali-metal cation with ring nitrogen in the transition state leading to formation of an orthio-quinonoidal σ-complex. Exclusive initial attack at the C-4 ring site appears to occur in the reaction of tetrafluoropyrimidine (5) with oximates 6a and 6c to afford 4-(MeC = NO)C₄F₃N₂ (12a) and 4-(PhCMe=NO)C₄F₃NN₂ (12b), respectively; Some further attack on product 12b by oximate 6c at the C-6 site takes place to give the disubstituted derivative 4,6-(PhCMe=NO)₂C₄F₂N₂ (13).     

Japanese试剂的环化反应

利用Japanese试剂与含活泼氢的双官能团化合物的环化反应,合成了含N-P-N,N-P-O的五元磷杂环化合物,并用IR,NMR和MS对新化合物进行了表征。     

Synthesis and Herbicidal Activity of Novel N-Allyloxy/Propargyloxy Aryloxyphenoxy Propionamide Derivatives

A series of novel N-allyloxy/propargyloxy aryloxyphenoxy propionamide compounds was designed and prepared. The structures of the synthesized compounds were confirmed by means of ¹H NMR, ¹³C NMR, LC-MS, elemental analysis and IR. The bioassay results indicate that when against Digitaria sanguinalis and Echinochloa crus-galli, (R)-N-(propargyloxy)-2-{4-[(6-chloroquinoxalin-2-yl)oxy]phenoxy}propanamide(1m)(IC₅₀=6.8 and 6.5 g/hm², respectively) and (R)-N-(allyloxy)-2-{4-[(6-chloroquinoxalin-2-yl)oxy]phenoxy}propanamide(1r)(IC₅₀=7.4 and 6.0 g/hm², respectively) are much more effective than commercial aryloxyphenoxypropionic ester herbicide clodinafop-propargyl(IC₅₀=46.5 and 14.6 g/hm², respectively). The results of crop selectivity show that compounds 1m and 1r are safe to soybean, rape and cotton and can be used as herbicides for soybean, rape and cotton crop.     

DETERMINATION OF SINGLET OXYGEN RATE CONSTANTS IN AQUEOUS SOLUTIONS

Abstract— A very efficient quenching of singlet oxygen (¹O₂) by N₃^- ions has been applied to the determination of rate constants of reactions of ¹O₂ with various substrates (A). This determination has been made possible by choosing experimental conditions which give simple competition between N₃^- and A for ¹O₂ formed in the steady state irradiation of convenient sensitizing dye (S). The consumption of oxygen by the substrate, as followed with an oxygen analyzer, decreases in the presence of low concentrations of N₃^-. Using neutral air saturated aqueous solutions containing the dye phenosafranine + A and varying concentrations of N₃^-, the ¹O₂ rate constants for reactions with biological substrates and some radiation protective agents have been determined.     

Synthesis, structure and spectroscopic study of Rh polypyridine complexes with phenylcyanamide derivative ligands

Several new Rh^III complexes, [Rh(tpy)(bpy)L](PF₆)₂ (tpy=2,2′:6′,2″-terpyridine, bpy=2,2′-bipyridine, and L=monoanions of phenylcyanamide(pcyd)), 4-methylphenylcyanamide (4-MePcyd), 2,4-dimethylphenylcyanamide (2,4-Me₂pcyd), 4-methoxyphenylcyanamide (4-MeOPcyd), 2-chlorophenylcyanamide (2-Clpcyd) and 2,5-dichlorophenylcyanamide (2,5-Cl₂pcyd) have been synthesized and characterized by elemental analysis, IR, ¹H NMR and electronic absorption spectroscopies. ORTEP drawing of [Rh(tpy)(bpy)(2,5-Cl₂pcyd)](PF₆)₂·1/2CH₃CN shows three pyridyl rings of the tpy ligand that are nearly coplanar, as are the two rings of bpy. The anionic cyanamide group is coordinated end-on by the nitrile nitrogen to the Rh^III. The Rh^III–NCN bond is bent, having an angle of 125.4°. This bent bond is largely determined by the σ-bonding interaction of a cyanamide non-bonding electron pair in a sp² hybrid orbital.     

Syntheses of Chiral Fused Heterocyclic Compounds Containing l,2,4-Triazole Ring

The chemistry of life is based considerably on chirality. Consequently, stereospecificity has to be regarded as an especially important characteristic of biological systems. The influence of stereospecificity of the biological activities of enzyme inhibitors or compounds binding to receptor is a well known fact in the field of drug action^[1]. s-Triazoles and l,3,4-thiadiazoles are reported to exhibit broad spectrum of biological and pesticidal activities^[2-3].In recent years, bridge head nitrogen heterocycles have received much attention as anthelmintic agents, however, it is not observed that the syntheses of chiral fused heterocyclic compounds containing s-triazoles and l,3,4-thiadiazoles. In order to study the relationship between stereochemistry and the performance of fungicides, we have synthesized a series of (s)-1,2-di(3-aryl-s-triazolo[3,4-b][1,3,4] thiadiazolo-6-yl) ethylamine and (s)-1-(3-aryl-s-triazolo[3,4-b][l,3,4] thiadiazolo-6-yl) ethylamine by the condensation of 3-aryl-4-amino-5-mercapto-1,2,4-triazoles with L-aspartic acid and L-alanine in the presence of phosphorusoxychloride.     

The mechanism of pyrolysis of polycycloalkyl sulfonates : The homo-retroene reaction in the noradamantane, adamantane and diamantane series

The minor product, 4-protoadamantene (5), from the gas phase pyrolysis of 2-adamantyl mesylate (3) was shown by labelling experiments not to arise from the major product, 2,4-dehydroadamantane (4), but rather by a concerted process (homo-retroene reaction). In the formation of 4, 1,3-elimination is favored by at least a 92:8 margin over a competitive route involving -elimination to a carbene and then C-H insertion. Equatorial and axial 2-noradamantyl mesylates pyrolyze to give predominantly 4-brendene (11) and triaxane (12), respectively, as required by concerted 1,3-eliminations, and not by an ion pair mechanism. The cross-over product appears in each case to result from the epimerizarion of the starting material by a wall-catalyzed process. In agreement with the results of the noradamantyl substrates, pyrolysis of 3-diamantyl mesylate (16) gave results which suggest that product stability helps to determine the course of the reaction. The products with the least amount of strain were obtained, namely 3,5-dehydrodiamantane (17) and pentacyclo[8.3.1.0^2,8.0^4,13.0^7,12]tetradec-5-ene (19, protodiamantene). The ease of separation of the cyclopropanic and olefinic products makes these reactions synthetically useful.     

Photochemische reaktionen von übergangsmetall-organyl-komplexen mit olefinen XI. Photochemisch induzierte C---C-verknüpfung von tricarbonyl-η-2,4-dimethyl-2,4-pentadien-1-yl-mangan mit 1-dimethylamino-2-propin—Synthese eines η-7-dimethylamino-N-2,4-heptadien-1-yl-chelatkomplexes

UV irradiation of tricarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-manganese (2) in THF at 208 K yields solvent-stabilized dicarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-tetrahydrofurane-manganese (3), which reacts in situ with two equivalents of 1-dimethylamino-2-propyne (4) to dicarbonyl-1–5-η-2,4-dimethyl-(6-dimethylaminomethyl-N)-10-dimethylamino-deca-2,4,6,8- tetraen-1-yl-manganese (5). The crystal and molecular structure was determined by an X-ray diffraction analysis. Complex 5 crystallizes in the monoclinic space group P2₁/c, A = 1109.9(2) pm, B = 836.0(2) pm, C = 2156.9(4) pm, β = 93.23(3)°, V = 1.9982(7) nm³, Z = 4. Complex 5 was also studied in solution by IR and NMR spectroscopy. A possible formation mechanism of 5 will be discussed.

Zusammenfassung

UV-Bestrahlung von Tricarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-mangan (2) in THF bei 208 K liefert solvenstabilisiertes Dicarbonyl-η⁵-2,4-dimethyl-2, 4-pentadien-1-yl-tetrahydrofuran-mangan (3), welches in situ mit zwei Äquivalenten 1-Dimethylamino-2-propin (4) zu Dicarbonyl-1–5-η-2,4-dimethyl-(6-dimethylaminomethyl-N)-10-dimethylamino-deca-2,4,6,8-tetraen-1-yl-mangan (5) reagiert. Seine Kristall- und Molekülstruktur wurde durch eine Röntgenbeugungsanalye bestimmt. Komplex 5 kristallisiert in der monoclinen Raumgruppe P2₁/c, A = 1109.9(2) pm, B = 836.0(2) pm, C = 2156.9(4) pm, β = 93.23(3)°, V = 1.9982(7)_ nm³, Z = 4. Komplex 5 wurde auch in Lösung IR- und NMR-spektroskopisch untersucht. Ein möglicher Bildungsmechanismus von 5 wird diskutiert.