Rearrangement of 3-membered 1,1,2-trifluorobromonium and iodonium ions and comparison of trifluorochloronium to fluorocarbenium ions

Reactions of chlorine (Cl(2)) with 4-halo-1,1,2-trifluorobut-1-enes (1, 2, or 3) give open-ion intermediates A and E that are in equilibrium. The open-chloronium ions (E) rearrange to a five-membered-ring halonium ion during ionic chlorination of 3 when the number-4 halo-substituent is iodine. Three-membered-ring bromonium and iodonium ions from alkenes 1, 2, or 3 are rather symmetrical and similar in structure. Quantum chemical calculations show that five-membered-ring halonium ion intermediates are 11 to 27 kcal/mol more stable than the three-membered-ring halonium ions or the open-ions A and E. The five-membered-ring intermediates lead to rearranged products. Rearranged products increase as the number-4 halogen (Z) becomes more nucleophilic (Z: Cl < Br < I). Open chloronium ions from ionic chlorination of terminal fluorovinyl alkenes are compared to the open ions generated by protons to similar alkenes.     

Simple and Simultaneous Determination of Free Chlorine, Free Bromine and Ozone in Water by LC

A simple liquid chromatographic method has been established for the simultaneous determination of free chlorine, free bromine, and ozone generated in electrical discharges. The method is based on the formation of organic derivatives, 4-halo-2,6-dimethylphenols with 2,6-dimethylphenol (2,6-DMP). The direct substitution reaction between halogens and 2,6-DMP was used for the determination of free chlorine, free bromine and ozone in water. For the determination of ozone, iodide was added 5 min after the addition of 2,6-DMP. The detection limits were about 2.0, 3.0 and 4.0 μg L^?1 for hypochlorite, hypobromite and ozone, respectively. The method was very simple and reproducible enough to permit the simultaneous analysis of each disinfectant in surface water or sea water in the presence of the mixture of disinfectants.     

蒎酮酸的卤代反应

国外对蒎酮酸的制备、反应及其衍生物的应用报道颇多。为了开发利用我国丰富的松节油资源,我们对顺式蒎酮酸(1)的卤代反应进行了研究。关于蒎酮酸的溴代反应已有研究,而氯代反应还未见报道。我们选用了氯气和氯化硫酰作为氯代反应试剂。在酸性条件下1与氯反应时,得到顺式-2,2-二甲基-3-氯乙酰基环     

Reactions of Substituted 2,3,7-Triazabicyclo[3.3.0]oct-3-ene-4-carboxylic Acid Esters with Halogens

Substituted 2,3,7-triazabicyclo[3.3.0]oct-3-ene-4-carboxylic acid esters react with chlorine and bromine to give the corresponding 4-halo-2,3,7-triazabicyclo[3.3.0]oct-2-ene-4-carboxylates. Heating of the latter to 120°C under reduced pressure leads to elimination of nitrogen molecule and formation of 6-halo-3-azabicyclo[3.1.0]hexane-6-carboxylates.     

Bromo-Derivatives of 2′-NHR-3,4-methylenedioxychalcone and Its 4-Quinolone Isomer

Bromination reaction of 2′-NHR-3,4′-methylenedioxychalcone (1) and 2,3-dihydro-2-(3′,4′-methylenedioxyphenyl)-4(1H)-quinolone (7) with bromine and N-bromosuccinimide are discussed. Depending on the character of the R group and on the reagent used nuclear or side-chain brominated or side-chain bromo-methoxylated products were obtained.     

Photolysis of bromo- and chloro-substituted benzyl derivatives. Competition between ionic and radical pathways

Photolysis of 1-fluoro-2-halo-1,2-diphenylethanes was studied in solutions of tetrahydrofuran, acetonitrile, and cyclohexane. The effect of free radical inhibitor and metal hydrides on products formation as well as their ratio was analyzed to elucidate the reaction pathway. In the first step homolytic C-X bond cleavage occurs from a single excited state, resulting in a biradical pair. Further reaction path depends on the type of the halogen bonded and on the solvent polarity. Electron transfer within the radical pair cage is apparently more rapid for bromides than for chlorides and is opposite as expected on the basis of the relative electronegativities of chlorine and bromine. As radicals approach each other, they fall into ionic or radical product channels. This is influenced by solvent polarity, resulting in the larger yield of ionic products in the case of acetonitrile as in the case of less polar cyclohexane.     

Addition of chlorine,bromine and bromine chloride to some α,β-unsaturated methyl esters

The additions of chlorine, bromine and bromine chloride to trans methyl 2-butenoate 1, trans methyl 2-methyl-2-butenoate 2 and methyl 3-methyl-2-butenoate 3 under ionic conditions were studied. Bromine chloride addition always gave as a major regioisomer the 2-bromo-3--chloro compound,almost quantitatively in the case of 3. The mechanism of bromonium ion ring-opening (S_N1 or S_N2) is discussed with respect to the double bond substitution and regioisomer proportions. The dihalo products were identified by MS, ¹H and ¹³C NMR.     

Alkyl Esters of 2-[5-Chloro(bromo)-6-methoxy-4-methylpyrimidinyl-2-oxy]alkanoic Acids

The reaction of a mixture of formaldehyde and sodium cyanide or of lactic acid nitrile with trimethyl(6-methoxy-4-methylpyrimidinyl-2)ammonium chloride give the 2-(6-methoxy-4-methylpyrimidinyl-2-oxy)alkanoic acid nitriles. They were subsequently converted to the corresponding alkyl esters by a Pinner reaction and then to their 2-(5-halo-6-methoxy-4-methylpyrimidinyl-2-oxy) derivatives using N-halosuccinimides.     

Functionalized polychloroarenes in the Bichwald ligand-promoted Suzuki cross-coupling

Palladium-catalyzed Suzuki cross-coupling of isomeric dichloroacetophenones with phenylboronic acid in the presence of 2-dicyclohexylphosphino-2′-(dimethylamino)-biphenyl (DavePHOS, a Buchwald ligand) affords the corresponding diphenylacetophenones in high yields. The reaction of pentachloroacetophenone with phenylboronic acid (1.1–2.5 equiv.) proceeds unselectively to give isomeric mono- and disubstitution products. In the case of 3,4-dichloroanisole, 3-positioned chlorine atom is preferably replaced, however, with excess phenylboronic acid 4′;-methoxy-1,1′;:2′;,1″-terphenyl is quantitatively formed.

     

The reactions of 4-dicyanomethylene-2-phenyl-4H-1-benzopyran and some benzologs with nucleophiles

4-Dicyanomethylene-2-phenyl-4H-1-benzopyran (1) reacts with primary amines under mild conditions to give 4-imino-3-alkyl-5-alkylimino-2-phenyl-3,4-dihydro-5H-[1]benzopyrano[3,4-c]-pyridine derivatives which, in turn, are hydrolyzed with acid to 4-imino-3-alkyl-2-phenyl-3,4-dihydro-5H-[1]benzopyrano[3,4-c]pyridin-5-ones. When more vigorous conditions are employed for the reactions of 1 with primary amines, Dimroth rearrangements take place and the products are derivatives of 4-alkyl- (or aryl)amino-5-alkyl- (or aryl)imino-2-phenyl-5H-[1]benzopyrano-[3,4-c]pyridine. The latter compounds are hydrolyzed by acid to the corresponding 5-pyridone derivatives. The reaction of 1 with piperidine gives 2-phenyl-4-piperidyl-5H-[1]benzopyrano-[3,4-c]pyridin-5-one. Sodium methoxide reacts with 1 to give 3-cyano-2-methoxy-4-(2-hydroxyphenyl)-6-phenylpyridine. Two benzologs of 1 have been allowed to react with primary and secondary amines and the products are analogous to those obtained from 1 .     

Studies on silyl furans. II. Halodesilylation of 2-trimethylsilyl-3,4-bis(methoxycarbonyl)furans

Reactions of 2-trimethylsilyl-3,4-bis(methoxycarbonyl)furans 1a,b with sulfuryl chloride, bromine, and iodine monochloride in acetonitrile afforded the corresponding 2-halo-3,4-bis(methoxycarbonyl)furans 2a-f via chloro-, bromo-, and iododesilylation in good yields, respectively. However, the reaction of 1a with bromine in carbon tetrachloride mainly gave 2-bromo- 2b and 2-bromo-5-trimethylsilyl-3,4-bis(methoxycarbonyl)furan ( 3 ) in 37% and 45% yields. Similarly, the reaction of 1a with iodine monochloride afforded 1a , 2-chloro- 2a and 2-iodo-3,4-bis(methoxycarbonyl)furan ( 2c ) in 50%, 27%, and 23% yield.     

Convenient Ring-Bromination of Alkylnaphthalenes using N-Bromosuccinimide in Acetonitrile

Abstract: Abstract. 1-Alkyl- and 2-alkylnaphthalenes are conveniently brominated in the 4-and 1-positions respectively using N-bromosuccinimide (NBS) in acetonitrile. The reactions are easy to perform and give higher chemical yields and better regioselectivity compared to brominations employing bromine/dichloromethane.     

Successive Replacement of Halogen Atoms in 4,6-Dihaloquinolines in Cross-coupling Reactions with Arylboronic Acids Catalyzed by Palladium and Nickel Complexes

Conditions were found where in 6-halo-4-quinolines (halogen = iodine, bromine, or chlorine) the halogen atoms were replaced in succession by similar or different aryl groups in cross-coupling reactions with arylboric acids catalyzed by palladium and nickel complexes. Basing on successive Suzuki reaction a convenient procedure was developed for preparation of diarylquinolines that did not require isolation of the intermediate monoarylation product and afforded almost quantitative yields of diarylquinolines.     

Reactions of Substituted Ethyl 1,2,3,4,4′,5′-Hexahydrospiro-[naphthalene-2,5′-pyrazole]-3′-carboxylates with Halogens

Substituted ethyl 1,2,3,4,4′,5′-hexahydrospiro[naphthalene-2,5′-pyrazole]-3′-carboxylates react with chlorine or N-bromosuccinimide to give spirocyclic substituted 3-halo-4,5-dihydro-3H-pyrazoles which lose nitrogen molecule on heating with formation of substituted spirocyclic 1-halocyclopropane-1-carboxylates. Heating of the title compounds with bromine in acetic acid results in opening of the spiro-fused six-membered ring to afford ethyl 4-aryl-5-[2-(2-carboxyphenyl)ethyl]pyrazole-3-carboxylates.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 7, 2005, pp. 1058–1063.Original Russian Text Copyright © 2005 by Molchanov, Korotkov, Kopf, Kostikov.     

Comparison of the electrophilic and free-radical addition of halogens with hexafluoro-1,3-butadiene and 1,3-butadiene

Ionic and photochemical reaction of chlorine (Cl₂), bromine (Br₂) and iodine monochloride (ICl) to hexafluoro-1,3-butadiene (1) and 1,3-butadiene (2) were carried out under conditions that would provide product distributions under controlled ionic or free-radical conditions. Product distributions for ionic reaction of Cl₂ and Br₂ with 1 are similar and suggest a weakly-bridged halonium ion species. Theoretical calculations support weakly-bridged chloronium and bromonium ions for both dienes 1 and 2. There are more of the 1,4-dihalo-2-butene products from ionic halogenation of 1 than 2 which correlates with the greater charge density on carbon-4 of halonium ions from 1. Ionic and free-radical reactions of ICl with 1 give 8 and 2% of 3-chloro-4-iodohexafluoro-1-butene and 4-chloro-3-iodohexafluoro-1-butene, respectively. The minor cis-1,4-dihalo-2-butene products from 1 and 2 are reported when formed.     

Reaction of aromatic aldehydes with β-dicarbonyl compounds in a catalytic system: Piperidinium acetate-1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid

Condensation of aromatic (heteroaromatic) aldehydes with 1,3-dicarbonyl compounds under the 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF₄]) ionic liquid-piperidinium acetate catalytic system (0.2 equiv. of each component) in the absence of a solvent affords, depending on the structures of the reagents, 2-arylidene derivatives of methyl acetoacetate and acetylacetone, diethyl 2,4-bis(trifluoroacetyl)-3-phenylpentanedioate, or dimethyl 2-aryl-4-hydroxy-6-oxocyclohexane-1,3-dicarboxylates. The reactions of the resulting 2-arylidene derivatives with O-methylisourea in the [Bmim][BF₄] ionic liquid produced methyl 2-methoxy-4-methyl-6-aryldihydropyrimidine-5-carboxylates and 1-(2-methoxy-4-methyl-6-phenyldihydropyrimidin-5-yl)ethanone (mixtures of 3,6- and 1,6-dihydro isomers), which were transformed into the corresponding 3,4-dihydropyrimidin-2(1H)-one derivatives. Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1199–1204, May, 2005.     

Stereochemistry of the halolactonisation reaction The reaction of cis- and trans- stilbene-2-carboxylic acids with halogens

The stereochemistry of the reaction of cis- and trans-stilbene-2-carboxylic acids with chlorine and bromine, yielding the two diastereoisomeric 3-phenyl-4-halo-3:4-dihydroisocoumarins (III) and (IV) has been investigated. The reactions are entirely stereospecific and involve intramolecular attack by the carboxyl group on an intermediate carbonium or halonium ion. The lactones (III) and (IV) yield the two 3-(-hydroxybenzyl) phthalides (V) and (VI), with retention of configuration. Thionyl chloride transforms (V) and (VI) into the 3-(-chlorobenzyl) phthalides (IX) and (X), with inversion. Steric effects are mainly responsible for the alternative formation of halolactones or normal dihalogenated derivatives in the reactions between unsaturated acids and halogens.     

Reactivity of pyrrole pigments. Part 5: Electrophilic substitution—Nitration and bromination—Of some pyrromethenones and 5-arylmethylene-3,4-dimethyl-3-pyrrolin-2-ones

Some 5-arylmethylene-3,4-dimethyl-3-pyrrolin-2-ones react with both bromine and nitronium tetrafluoroborate (NO₂BF₄) to give 5-(aryl)nitromethylene-3-pyrrolin-2-ones and 5-(aryl)bromomethylene-3-pyrrolin-2-ones, respectively. The use of bromine in methanol affords 5-(aryl)bromomethyl-3,4-dimethyl-5-methoxy-3-pyrrolin-2-ones. Whereas pyrromethenones react mainly on the pyrrole ring, ethyl 3,4-demethyl-5-[(3,4-dimethyl-5-oxo-3-pyrrolin-2-yl)methylene]-1H-pyrrole-2-carboxylate reacts as the aryl derivatives, however, with bromine in methanol the addition of two methoxy groups at the exocyclic double bond takes place. 3,4-Dimethyl-5-(2-pyridylmethylene)-3-pyrrolin-2-one does not react with bromine or NO₂BF₄, but reacts as the aryl derivatives with bromine in methanol. The reactivity patterns are in agreement with the theoretical ones obtained from MINDO/3 calculations, using theFukui frontier orbital model. The obtained results are used to explain the reactivity of rubins (biladienes-a,c) and verdins (bilatrienes-a,b,c) in front of electrophiles.Einige 5-Arylmethylen-3,4-dimethyl-3-pyrrolin-2-one reagieren sowohl mit Brom als auch mit Nitroniumtetrafloroborat (NO₂BF₄). Man erhält 5-(aryl)bromomethylen-oder 5-(aryl)nitromethylen-3-pyrrolin-2-one. Bei Verwendung einer methanolischen Bromlösung werden 5-(aryl)bromomethyl-3,4-dimethyl-5-methoxy-3-pyrrolin-2-one gebildet. Pyrromethenone reagieren hauptsächlich am Pyrrolring, Ethyl 3,4-dimethyl-5-[(3,4-dimethyl)-5-oxo-3-pyrrolin-2-yl)methylen]-1H-pyrrol-2-carboxylat hingegen verhält sich wie ein Arylderivat, mit methanolischen Bromlösung jedoch erfolgt Eintritt zweier Methoxygruppen an der exocyclischen Doppelbindung.5-(2-Pyridyl)methylen-3,4-dimethyl-3-pyrrolin-2-on reagiert nicht mit Brom oder NO₂BF₄, wohl aber mit einer methanolischen Bromlösung und verhält sich unter diesen Bedingungen wie ein Arylderivat; 3- und 4-Pyridylderivate verhalten sich analog. Die Reaktivität ist in Übereinstimmung mit theoretischen Werten aus MINDO/3-Rechnungen unter Verwendung des Fukui frontier orbital model. Die Reaktivität von Rubinen (Biladiene-a, c) und Verdinen (Bilatriene-a,b,c) gegenüber Elektrophilen werden im Zusammenhang mit den erhaltenen Resultaten diskutiert.

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Reaktivität der Pyrrolpigmente, 5. Mitt.: Elektrophile Substituierung (Nitrierung und Bromierung) von einigen Pyrromethenonen und 5-Arylmethylen-3,4-dimethyl-3-pyrrolin-2-onen

     

1-Sulfopyridinium chloride:Green and expeditious ionic liquid for the one-pot synthesis of fused 3,4-dihydropyrimidin-2(1H)-ones and thiones under solvent-free conditions

1-Sulfopyridinium chloride portrayed as an efficient and recyclable ionic liquid for the synthesis of fused3,4-dihydropyrimidin-2(1H)-ones and thiones via a modified Biginelli reaction involving one-pot three component condensation of 6-methoxy-1-tetralone,arylaldehydes and urea/thiourea under solventfree conditions.Analytically pure products are formed within 10–20 min in excellent yields.     

Synthesis of α-halo-α,α-difluoromethyl ketones by a trifluoroacetate release/halogenation protocol

Three series of α-halo-α,α-difluoromethyl ketones are prepared from highly α-fluorinated gem-diols by exploiting the facile release of trifluoroacetate, followed by immediate trapping of the liberated α,α-difluoroenolate with an electrophilic chlorine, bromine, or iodine source. The products are typically isolated in good yields, even in the case of sensitive, α-iodo-α,α-difluoromethyl ketones. Also, we demonstrate that an α-iodo-α,α-difluoromethyl ketone will participate in a copper-promoted reaction to forge a new carbon-carbon bond.