Copper tetrafluoroborate

Corey reported one of the earliest examples of dienophile activation by a copper Lewis acid (Sch. 42) [80]. The copper tetrafluoroborate coordinates to the cyano group and facilitates the Diels-Alder reaction without marked isomerization of the diene. 

Applying oxygen electrodes the production of the tetrafluoroborate delivers no side-products and needs less energy than compared to traditional processes based on the reaction of tin with copper tetrafluoroborate. An additional advantage of this process consists in the fact that the cell does... 

Reaction with Copper Perchlorate, Ferric Perchlorate, Copper Tetrafluoroborate, or Thallium Trifluoroacetate... 

Neither copper perchlorate nor ferric perchlorate reacts with thiophene to yield a conducting polymer. However, electrically conductive polymers are synthesized by the reaction of 3-methylthiophene or bithiophene with ferric perchlorate. With copper perchlorate, only bithiophene undergoes a simultaneous polymerization and oxidation reaction. X-ray photoelectron spectroscopy of the PT derivatives with perchlorate as counter ion indicates that a significant amount of the chlorine may be covalently bonded to the polymer [288, 574], The electrical conductivity of polymerized bithiophene reaches values as high as 4.5 S cm [574]. 3-Dodecyl-2,2 -bithiophene, 3-(3-phenylpropyl)thiopheneand 3,4-dibutoxythiophene can be polymerized oxidatively using either copper perchlorate, copper tetrafluoroborate, or ferric perchlorate [575]. 

In the first Corey prostaglandin synthesis we saw the use of an acyl anion equivalent . Now we will see another application of the equivalency concept , use of a real reactant that, after some functional group manipulations, can be used to accomplish a transformation that could not be accomplished otherwise. Let s look at the tactics that were ultimately used by the Corey group. Sodium cyclopentadienide was alkylated with chloromethyl methyl ether to provide 37. Chloromethyl methyl ether is extremely reactive and thus, this reaction could be accomplished at a low temperature, below the temperature at which 37 isomerizes to cyclopentadienes 38 and 39. Cyclopentadiene 37 was then reacted with an excess of 2-chloroacrylonitrile, an extremely reactive dienophile. Under the influence of Lewis acid promotion (copper tetrafluoroborate) this diene-dienophile pair underwent cycloaddition, to give 40 at temperatures where diene isomerization did not occur. Although 40 was obtained as a mixture of endo and exo diasteromers, it is notable that the dienophile approached 37 from the sterically least... 

Compounds containing fluorine and chlorine are also donors to BF3. Aqueous fluoroboric acid and the tetrafluoroborates of metals, nonmetals, and organic radicals represent a large class of compounds in which the fluoride ion is coordinating with trifluoroborane. Representative examples of these compounds are given in Table 5. Coordination compounds of boron trifluoride with the chlorides of sodium, aluminum, iron, copper, 2inc, tin, and lead have been indicated (53) they are probably chlorotrifluoroborates. 

Technetium-9 9m sestamibi is used in myocardial perfusion imaging for the evaluation of ischemic heart disease. It is prepared from a lyophilized kit containing tetrakis(2-methoxy isobutyl isonittile) copper(I) tetrafluoroborate stored under nitrogen. Upon reconstitution with up to 5.6 GBq (150 mCi) of 99mTc pertechnetate, the product is formed by boiling for 10 minutes. 

With ten 7i-electrons delocalized over seven atoms, trithiadiazepine is electron rich and should undergo electrophilic substitution, which indeed it does. Nitronium tetrafluoroborate at — 10 C or copper(II) nitrate gives the mononitro derivative 5, which can be converted into the dinitro compound 6 by the action of an excess of nitronium tetrafluoroborate at 10 C.388... 

On the other hand, Hartman and Biffar (1977) observed that the decomposition of several arenediazonium tetrafluoroborates in methylene chloride was catalyzed by the addition of 10 mol% of dicyclohexane-18-crown-6 and powdered copper, but not by copper alone nor by the crown ether and powdered glass. 

Arylation of activated double bonds with diazonium salts in the presence of copper catalysts is known as the Meerwin reaction. The reaction is postulated to either proceed through an organocopper intermediate or through a chlorine atom transfer from chiral CuCl complex to the a-acyl radical intermediate. Brunner and Doyle carried out the addition of mesityldiazonium tetrafluoroborate with methyl acrylate using catalytic amounts of a Cu(I)-bisoxazoline ligand complex and were able to obtain 19.5% ee for the product (data not shown) [79]. Since the mechanism of the Meerwin reaction is unclear, it is difficult to rationalize the low ee s obtained and to plan for further modifications. 

Table 3 Mean values and ranges (in parentheses) for the hydrogen-bonded contacts in the extended structures of the structurally characterised bis(AT-alkylamidino-0-alkylurea)copper(II) nitrates, tetrafluoroborates, halides and sulfates...

On the other hand, Hartman and Biffar (1977) reported that decomposition of arenediazonium tetrafluoroborates in dichloromethane in the presence of copper metal is catalysed by dicyclohexyl- 18-crown-6. Electron-withdrawing substituents in the aryl ring enhance the rate of the reaction. The main function of the crown ether is probably to solubilize the salt. The effect of the complexation on the rate was not investigated in detail. Similar enhanced solubilization of diazonium salts in apolar solvents was reported and used by Martin and Bloch (1971) in pyrolysis experiments aimed at the generation of the dehydrocyclopentadienyl anion. 

Compounds 133, prepared by the condensation of benzotriazole with aldehydes R HO (R1 = H, Pr or Ph) and 7V-octylaminoacetonitrile, react with sodium tetrafluoroborate to give the cyanomethyl derivatives 134. The latter are de-cyanomethylated by the action of copper(II) sulphate. Treatment of 133 with Grignard reagents affords the analogues 135 (R2 = Ph or PhCH2) and thence the secondary amines 136130. 

There are a few reports of poly(naphthalene) thin films. Yoshino and co-workers. used electrochemical polymerization to obtain poly(2,6-naphthalene) film from a solution of naphthalene and nitrobenzene with a composite electrolyte of copper(II) chloride and lithium hexafluoroarsenate. Zotti and co-workers prepared poly( 1,4-naphthalene) film by anionic coupling of naphthalene on. platinum or glassy carbon electrodes with tetrabutylammonium tetrafluoroborate as an electrolyte in anhydrous acetonitrile and 1,2-dichloroethane. Recently, Hara and Toshima prepared a purple-colored poly( 1,4-naphthalene) film by electrochemical polymerization of naphthalene using a mixed electrolyte of aluminum chloride and cuprous chloride. Although the film was contaminated with the electrolyte, the polymer had very high thermal stability (decomposition temperature of 546°C). The only catalyst-free poly(naphthalene) which utilized a unique chemistry, Bergman s cycloaromatization, was obtained by Tour and co-workers recently (vide infra). 

However, radical intermediates cannot be definitely excluded, at least not in the reaction of pyiylium salts in pyridine. Steuber showed that such pyrylium salts as 2.4.6-triphenyl-pyrylium-or 2.4.6-tri-tert-butyl-pyrylium-tetrafluoroborate can be reduced to stable pyryl radicals 32 by pyridine this reduction proceeds particularly smoothly if traces of copper powder are added. 

Copper(I) oxide allows dediazoniation of 4-hydroxybenzenediazonium tetrafluoroborate in hydrogen fluoride (60%)/pyridine at a temperature as low as 90°C,89 but the yield (23%) cannot compete with the yield delivered by fluorodediazoniation at 140°C in the same medium without copper(I) oxide (59 %). 

Substituted l,2,4-thiadiazol-5-yl diazonium tetrafluoroborates (314) react with potassium halides in acetonitrile in the absence of catalysts to afford the corresponding 5-halogeno compounds (315) in excellent yields.169 The isomeric 5-phenyl-l,2,4-thiadiazol-3-yl diazonium salts, however, resist substitution by this procedure, except with iodide ions by taking advantage of the catalytic effect of copper... 

As predicted by the soft acid behaviour36 of copper(I), very few examples of the fluoride ion coordinated to copper(I) are known (Table 16). It occurs on the fluoride ion in [Cu(PPh3)3F],37 and on the coordinated tetrafluoroborate anion in [Cu(PPh3)3(FBF3)] (4) 67 in both cases a tetrahedral CuP3F chromophore is present. 

It has been reported that diphenyliodonium triflate reacts with the lithium enolates of some cyclic ketones in the presence of copper cyanide to yield the corresponding a-phenylated or a-diphenylated ketones.58 There has been a detailed analysis of the products of thermal decomposition of diphenyliodonium tetrafluoroborate and hexafluorophosphate salts.59... 

DIELS-ALDER CATALYSTS Alkylaluminum halides. Alumina. Aluminum chloride. Bomyloxyaluminum chloride. Copper(n) acetate-Copper(II) tetrafluoroborate. 3-Cyclodextrin. 

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