2,3,5,6-Tetramethylmorpholine. I

The separation and characterization of the six possible isomers of 2,3,5,6-tetramethylmorpholine are described. Synthetic routes for the preparation of any isomer in fair yield from easily accessible intermediates are reported.     

An Efficient Synthesis of 2,3,5,6-Tetramethylidene-7-oxanorbornane

Palladium-catalyzed double carbomethoxylation of the Diels-Alder adduct of furan and maleic anhydride yielded the methyl all-exo-7-oxanorbornane-2,3,5,6-tetracarboxylate (7) which was transformed in three steps into 2,3,5,6-tetramethylidene-7-oxanorbornane (1) , a useful synthon. Six isomeric methyl 7-oxanor-bornane-2,3,5,6-tetracarboxylates (7–12) have been isolated and their ¹H- and ¹³C-NMR. data are compared.     

1,2-Dimethyl-1,2-diphenyidisilane-1,2-diol and its K,Na, and FeII derivatives. Molecular structure of the all-trans-isomer, 2,3,5,6-tetra-methyl-2,3,5,6-tetraphenyl-1,4-dioxa-2,3,5,6-tetrasilacyclohexane

Hydrolysis of 1,2-dimethyl-1,2-diphenyl-1,2-dichlorodisilane yields 1,2-dimethyl-1,2diphenyldisilane-1,2-diol, which undergoes dimerization into stereoisomeric 2,3,5,6-tetramethyl-2,3,5,6-tetraphenyl-1,4-dioxa-2,3,5,6-tetrasilacyclohexanes under the action of H₂SO₄. Pure all-trans-isomer has been isolated and characterized by¹H NMR and IR spectroscopy and X-ray analysis. The reaction of sodium disilanediolate with FeBr₂ results in the formation of 1,2-dimethyl-1,2-diphenyl-4-ferra(ii)-3,5-dioxa-1,2-disilacyclopentane.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2550–2556, October, 1996.     

2,3,5,6-Tetrafluorbenzoldisulfonsäure aus pentafluorbenzolsulfonsäure

The sulfonation of pentafluorobenzene with liquid SO₃ to pentafluorbenzenesulfonic acid at normal pressure as well as its conversion to 1-thiol-2,3,5,6-tetrafluorobenzenesulfonic acid, 2,3,5,6-tetrafluorobenzenedisulfonic acid monochloride and 2,3,5,6-tetrafluorobenzenedisulfonic acid are described. The preparation of anhydrous pentafluorobenzenesulfonic acid and 2,3,5,6-tetrafluorobenzenedisulfonic acid is described.     

2,3,5,6-四氟苯甲醇的合成

经氟代、水解脱羧、酯化、还原等步骤合成了杀虫剂四氟苯菊酯的重要中间体2,3,5,6-四氟苯甲醇, 改进了氟代反应的无水操作和反应条件, 产物四氟对苯二甲腈纯度高达98.3%, 通过加入水参与反应改进了水解反应, 使水解和脱羧由两步反应变为一步, 且产物为只脱一个羧基的2,3,5,6-四氟苯甲酸, 收率可以高达92.5%, 用相对价廉的NaBH₄/I₂体系还原2,3,5,6-四氟苯甲酸甲酯以52.3%的收率得到了目标产物, 总收率29.6%.     

Some reactions of diethyl 2,3,5,6-tetrachloropyridin-4-ylmalonate

The acid and alkaline hydrolysis of diethyl 2,3,5,6-tetrachloropyridin-4-ylmalonate has been studied. A method has been developed for obtaining diethyl (2,3,5,6-tetrachloropyridin-4-yl) alkylmalonates.Translated from Khimiya Geterotsiklicheskikh Soedinii, Vol. 6, No. 6, pp. 791–793, June, 1970.     

Spectrophotometric assay of yeast vitality using 2,3,5,6-tetramethyl-1,4-benzoquinone and tetrazolium salts.

A method for the spectrophotometric assay of yeast vitality was developed using 2,3,5,6-tetramethyl-1,4-benzoquinone and tetrazolium salts. The metabolic efficiency of 2,3,5,6-tetramethyl-1,4-benzoquinone by yeast cells was used as an index of yeast vitality. 2,3,5,6-Tetramethyl-1,4-benzoquinone was reduced to 2,3,5,6-tetramethyl-1,4-hydroquinone by yeast cells. Then, the superoxide anion radicals generated from O2 by reduction with 2,3,5,6-tetramethyl-1,4-hydroquinone under alkaline conditions reduced tetrazolium salts to formazan, which exhibited absorbance maxima at 440 nm. A linear relationship between the absorbance and viable cell density was obtained in the range of 1.0 x 10(5)-2.0 x 10(7) cells/ml for a sample solution. During the cultivation of yeast cells, the absorbance showed almost an anti-parallel change with that of glucose in yeast growth and fermentation, suggesting that the absorbance change reflected the vitality of yeast cells.     

4-Oxo-2,3,5,6-tetrafluorocyclohexa-2,5-dienylidene--a highly electrophilic triplet carbene

The 4-oxocyclohexa-2,5-dienylidenes are an interesting class of highly electrophilic carbenes. We investigated the reactivity of the 2,3,5,6-tetrafluorinated and -tetrachlorinated derivatives 1b and 1c with small molecules under conditions of matrix isolation. The reactions with molecular oxygen and with carbon monoxide produce the expected carbonyl O-oxides and ketenes, respectively. As a result of the extreme electrophilicity of 1b and c both carbenes insert with no or very small activation barriers into H2 or the CH bonds of hydrocarbons. Obviously, spin restrictions for these formally spin-forbidden reactions do not result in substantial thermal activation barriers.     

The reaction of chloromagnesium bis(2,3,5,6-tetrachlorophenyl)copper with butyllithium

Chloromagnesium bis(2,3,5,6-tetrachlorophenyl)copper, prepared from two equivalents of 2,3,5,6-tetrachlorophenylmagnesium chloride and one equivalent of copper(I) chloride inTHF, reacts with one equivalent of butyllithium at –78°C to give, subsequent to derivatisation with chlorotrimethylsilane and then with acetyl chloride, (1-acetyl-2,3,5,6-tetrachlorophenyl)trimethylsilane (20%), 1-(trimethylsilyl)-2,3,5,6-tetrachlorobenzene (17%) and 1-acetyl-2,3,5,6-tetrachlorobenzene (34%) along with some trace products. The formation of these products is explained on the basis of the intermediate formation of chloromagnesium bis(1-lithio-2,3,5,6-tetrachlorophenyl)copper, a functionalised cuprate reagent.

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Die Reaktion von Chlormagnesium-bis(2,3,5,6-tetrachlorphenyl) kupfer mit Butyllithium

Zusammenfassung Chlormagnesium-bis(2,3,5,6-tetrachlorphenyl)kupfer, das aus zwei Äquivalenten 2,3,5,6-tetrachlorphenylmagnesiumchlorid und einem Äquivalent Kupfer(I)chlorid inTHF hergestellt wurde, ergab mit einem Äquivalent Butyllithium bei — 78 °C nach Derivatisierung mit Chlortrimethylsilan und dann mit Acetylchlorid folgende Produkte: (1-Acetyl-2,3,5,6-tetrachlorphenyl)trimethylsilan (20%), 1-(Trimethylsilyl)-2,3,5,6-tetrachlorbenzol (17%) und 1-Acetyl-2,3,5,6-tetrachlorbenzol (34%) neben einigen weiteren Produkten in Spuren. Die Bildung der genannten Produkte wird mit Chlormagnesium-bis(1-lithio2,3,5,6-tetrachlorphenyl)kupfer, einem funktionalisierten Cuprat-Reagens, als intermediär gebildeter Verbindung erklärt.

     

Synthetic utility of 4-bromo-2,3,5,6-tetrafluoropyridine

The regiochemistry of nucleophilic substitution of 4-bromo-2,3,5,6-tetrafluoropyridine has been investigated. Efficient, regioselective reactions occur with alkylamine, benzylamine and alkoxide nucleophiles, yielding products where substitution occurs ortho to the ring nitrogen. The resulting 2-substituted-4-bromo-3,5,6-trifluoropyridines can be functionalised further, either by a second regioselective nucleophilic displacement or palladium catalysed elaboration at the 4-position. Reactions with aromatic N-nucleophiles yield mixtures of ortho- and para-substituted products.     

Carbon-13 NMR studies of twenty-four methyl-substituted morpholines

Carbon-13 NMR spectra of all the isomers of monomethyl-, 2,3-, 2,5-, 2,6-, 3,5-dimethyl-, 2,3,5-, 2,3,6-trimethyl- and 2,3,5,6-tetramethylmorpholine have been obtained at both ambient (25 °C) and low temperature (～ ?100 to ?120 °C). The ring carbon shifts appear to be additive with respect to the position of the methyl groups. A good correlation between predicted and experimental shift values was obtained (r = 0.998₉). The values were used in an attempt to assign, conformationally, the ‘all cis’ isomer 2,3,5,6-tetramethylmorpholine, which from ¹HNMR spin–spin coupling studies has been unsuccessful. Methyl carbon shifts to high field were found for axially oriented carbons. The extracted ‘steric shift’ values for such carbons were compared to their corresponding proton shift data.     

2,3,5,6-Tetra(vinylthio)difluorobenzene in Reactions with Difunctional Nucleophiles

Reaction of 2,3,5,6-tetra(vinylthio)difluorobenzene with ethylene glycol affords 1,4-bis[2,3,5,6-tetra(vinylthio)-4-fluorophenoxy-1-ethyloxy-]-2,3,5,6-tetra(vinylthio)benzene, with diethylene glycol arises 2,3,5,6-tetra(vinylthio)-4-(4-hydroxyethoxyethyloxy)-1-fluorobenzene, with 1,5-diaminopentane forms 1,5-bis[2,3,5,6-tetra(vinylthio)-4-fluoroanilino]pentane; in reactions with 2-aminoethanethiol and 2-mercaptoethanol occurs substitution of two fluorine atoms by RS groups.     

Facile synthesis of 2,3,5,6-tetrabromo-4-methyl-nitrocyclohexa-2,5-dien-1-one, a mild nitration reagent

Nitrocylcohexadienones have been applied as nitration reagents for mild, mono-nitrating reactions. The original synthesis of 2,3,5,6-tetrabromo-4-methyl-4-nitrocylcohexa-2,5-dien-1-one appeared to be difficult to pursue due to both the solvent system and reaction conditions. Therefore, we applied a modified solvent system and optimized the reaction conditions to prepare the dienone at 0°C, eventually overcome the difficulties.     

Reactions of Polyhalopyridines. 16. Synthesis and Reactions of 2,3,5,6-Tetrafluoro-4-perfluoroalkylthiopyridines

Identical reaction products, viz. 2,3,5,6-tetrafluoro-4-perfluoroalkylthiopyridines 3a-c, were obtained on thermal decomposition of Xe(II) bisperfluoroalkylcarboxylates in the presence of mercaptotetrafluoropyridine and bis(2,3,5,6-tetrafluoro-4-pyridyl) disulfide. Compounds 3a-c readily interact with N-, O-, and S-containing nucleophiles, though with the first two types of reactant only with substitution of fluorine atoms in position 2 of the pyridine ring. In the latter case products are obtained both with retention of the perfluoroalkylthio group on interaction with sodium N,N-dimethyldithiocarbamate, and with total fission of that group in the case of alkali metal methanethiolate and toluenethiolate.     

3,3-Dimethyl-2,3,5,6-tetrahydroimidazo[2,1-b][1,3,4]thiazasilole and Its Derivatives with Five-Coordinate Silicon Atom

Previously unknown 3,3-dimethyl-2,3,5,6-tetrahydroimidazo[2,1-b][1,3,4]thiazasilole and its zwitterionic derivatives containing five-coordinate silicon atom, namely 7-substituted 3,3-dimethyl-2,3,5,6-tetrahydroimidazo[2,1-b][1,3,4]thiazasilol-4-ium chlorides, have been synthesized by reaction of 1,3-bis(trimethylsilyl)tetrahydroimidazole-2-thione with chloro(chloromethyl)dimethylsilane and subsequent transformations of the products.     

Synthesis and mesomorphic properties of 4-[(4-n-polyfluoroalkoxy-2,3,5,6-tetrafluorophenyl)ethynyl]phenyl fluoro-substituted benzoates

A series of 4-[(4-n-polyfluoroalkoxy-2,3,5,6-tetrafluorophenyl)ethynyl]phenyl fluoro-substituted benzoate liquid crystals have been synthesized. Their phase transition temperatures have been measured by optical polarizing microscopy and confirmed by DSC. The results show that a highly fluorinated terminal chain impairs mesomorphic properties.     

Synthesis and mesomorphic properties of 4-[(4-n-polyfluoroalkoxy-2,3,5,6-tetrafluorophenyl)ethynyl]phenyl fluoro-substituted benzoates

A series of 4-[(4-n-polyfluoroalkoxy-2,3,5,6-tetrafluorophenyl)ethynyl]phenyl fluoro-substituted benzoate liquid crystals have been synthesized. Their phase transition temperatures have been measured by optical polarizing microscopy and confirmed by DSC. The results show that a highly fluorinated terminal chain impairs mesomorphic properties.     

Thermally stable polymers derived from 2,3,5,6-tetraaminopyridine

The stable trihydrochloride salt of 2,3,5,6-tetraaminopyridine (TAP) has been found to be a versatile intermediate to a variety of thermally stable polymers such as polybenzimidazoles (PBI), polyimidazopyrrolones (pyrrones), and polybenzimidazobenzophenanthroline (BB polymer). The controlled reactivity of two of the four amino sites of TAP · 3HCl towards diacid halides and dianhydrides makes possible the preparation of high molecular weight, soluble polyamide prepolymers at mild temperatures. PBI, pyrrones, and BB polymer are obtained from the linear polyamide precursors by heating at 150–375°C. Unoptimized cyclized polymers were aged isothermally in air at 600°F (316°C) and found to be superior to analogous polymers described in the literature. Weight retentions of up to 97% were observed after 500 hr in air at 600°F.     

Synthesis and properties of 1-bromo-2,3,5,6-tetrakis(3-pentyl)benzene: a highly sterically hindered aryl bromide

The preparation of 1-bromo-2,3,5,6-tetrakis(3-pentyl)benzene is reported. The ¹H and ¹³C NMR spectra indicate the presence of rotational isomers at room temperature which interconvert on heating. Coalescence of the NMR peaks for the methine and methylene aliphatic protons is observed at 100–120 °C. The conversion of this aryl bromide to the corresponding aryllithium is reported. Similar but less bulky aryl bromides have also been synthesised.     

The synthesis and phase transition of 4''''-methylphenyl 4"-[(4-alkoxy-2,3,5,6-tetrafluorophenyl)ethynyl]benzoates

A homologous series of 4'-methylphenyl 4"-[(4-alkoxy-2,3,5,6-tetrafluorophenyl)ethynyl]-benzoates have been synthesized. Polarizing microscopic textural observation shows that such compounds exhibit enantiotropic nematic phase.