Vinyl tetrafluoroborates

Vinylboronic acids and vinyl tetrafluoroborates can be trifluoromethylated under conditions allowing for a one-electron reduction (see below for mechanistic details). Under similar conditions, unsaturated carboxylic acids undergo decarboxylative trifluoromethylation, leading to the formation of vinylic CF3 derivatives (Scheme 9) [30, 33-37]. 

Sodium P-chloroethanesulfonate [15484-44-3] can be obtained by reacting vinyl chloride with sodium bisulfite [7631-90-5] (66). Reaction with nitronium tetrafluoroborate [13826-86-3] yi ds l-chloro-l- uoro-2-nitroethane [461-70-1] (67). 

Lithium fefrafc/s-(3,5-ditrifluoromethyl)borate, which provides an unsolvated lithium cation in noncoordinating solvents, exhibits a several thousandfold catalysis of the reaction of cyclopentadiene and methyl vinyl ketone.37 Lithium tetrafluoroborate is also an effective catalyst and in some instances has worked when LiC104 has failed, such as in the intramolecular reaction shown below.38... 

A basic ionic liquid, l-methyl-3-butylimidazolium hydroxide ([bmIm]OH) and l-butyl-3-methyl-methylimidazolium tetrafluoroborate ([bmim]BF4), has been introduced as a catalyst and reaction medium for the Markovnikov addition of imidazoles 116 to vinyl esters 115 under mild conditions to give imidazoesters 117 <06JOC3991 06TL1555>. A series of (nitroimidazolyl)succinic esters and diacids were prepared from the Michael-type addition of the nitroimidazole to the a,P-unsaturated ester <06S3859>. 

Barluenga et al. developed a novel exo-endo-cyclization of a,codiynes by use of bis(pyridyl) iodonium(I)-tetrafluoroborate (IPy2BF4) as catalyst.1171 The reaction follows a cationic-cationic pathway (scheme 6). First the electrophilic iodo ion reacts with the triple bond of 26 to give the relative stable vinyl cation 28. Ring closure leads to a seven-... 

Photosolvolysis of some vinyl iodonium substrates can be compared with thermal solvolysis of the same substrates. Photochemical reaction of (E)- and (Z)-2-phenylprop-l-enyl(phenyl)iodonium tetrafluoroborate (31) in methanol and TFE gave products of heterolytic cleavage of vinylic C-I bond as summarized in Table III (for the product structures see eq 14.17 In contrast to... 

Comparisons of product distributions in thermal and photochemical solvolyses show that the primary vinyl cation is not involved in thermolysis but is formed photochemically. The chirality probe approach using optically active 4-methylcyclohexylidenmethyl(aryl)iodonium tetrafluoroborate 19 was applied to the photosolvolysis.24 The rearranged product 4-methylcycloheptanone retained some optical activity, but the enantiomeric product in slight excess has a different structure depending on the iodoarene leaving group Arl of the substrate. The results indicate that the primary vinyl cation involved is not in a free, dissociated achiral form. 

Cyclohexenyl and cyclopentenyl iodonium tetrafluoroborates were also photolyzed in methanol. Ring-strained five-membered cyclic vinyl cation could be generated photochemically as well as the six-membered cyclic vinyl cation.25... 

Volume 75 concludes with six procedures for the preparation of valuable building blocks. The first, 6,7-DIHYDROCYCLOPENTA-l,3-DIOXIN-5(4H)-ONE, serves as an effective /3-keto vinyl cation equivalent when subjected to reductive and alkylative 1,3-carbonyl transpositions. 3-CYCLOPENTENE-l-CARBOXYLIC ACID, the second procedure in this series, is prepared via the reaction of dimethyl malonate and cis-l,4-dichloro-2-butene, followed by hydrolysis and decarboxylation. The use of tetrahaloarenes as diaryne equivalents for the potential construction of molecular belts, collars, and strips is demonstrated with the preparation of anti- and syn-l,4,5,8-TETRAHYDROANTHRACENE 1,4 5,8-DIEPOXIDES. Also of potential interest to the organic materials community is 8,8-DICYANOHEPTAFULVENE, prepared by the condensation of cycloheptatrienylium tetrafluoroborate with bromomalononitrile. The preparation of 2-PHENYL-l-PYRROLINE, an important heterocycle for the synthesis of a variety of alkaloids and pyrroloisoquinoline antidepressants, illustrates the utility of the inexpensive N-vinylpyrrolidin-2-one as an effective 3-aminopropyl carbanion equivalent. The final preparation in Volume 75, cis-4a(S), 8a(R)-PERHYDRO-6(2H)-ISOQUINOLINONES, il lustrates the conversion of quinine via oxidative degradation to meroquinene esters that are subsequently cyclized to N-acylated cis-perhydroisoquinolones and as such represent attractive building blocks now readily available in the pool of chiral substrates. 

Blechert and co-workers successfully employed the [4 -I- 2] cycloaddition for the transformation of indole derivatives [79-81], For instance, using 2-vinyl-indole derivatives as heterodienes, (3-acceptor-substituted cyclic and acyclic ena-mines (dienophile), and triarylpyrylium tetrafluoroborate as the photosensitizer, the corresponding Diels-Alder adducts were formed in moderate to good yields with complete regiochemical and stereochemical control [79], Alternatively, good results could be obtained in the reaction of indoles and exocyclic 1,3-dienes, thus providing an easy excess to multifunctionalized carbazoles [80], Quantum... 

Dicarbonyl(cyclopentadienyl) (ethyl vinyl ether)iron tetrafluoroborate Iron(l+), dicarbonyl (n -2,4-cyclopentadien-l-yl )[(l,2-Ti)-ethoxyethene]-, tetrafluoroborate(l-) (10) (75182-42-2)... 

Palladium-catalyzed arylation of the electron-rich olefin bntyl vinyl ether has been accomplished in the ionic liquid l-butyl-3-methylimidazolium tetrafluoroborate using as the arylating agents aryl iodides and bromides instead of the commonly used, but commercially unavailable and expensive, aryl triflates. The reaction proceeds with high efficiency and remarkable regioselectivity, leading almost exclnsively to substitution by various aryl groups at the olefinic carbon a to the heteroatom of butyl vinyl ether (Xu et ak, 2001). 

The block copolymer of ethylene oxide and 3,3-dimethylthietane shows useful properties of complexing halogen and heavy metal salts (79MI51402). Thietanes can be polymerized with methylmagnesium iodide as well as with a variety of electrophiles such as methyl sulfate, trimethyloxonium tetrafluoroborate, triethylaluminum, boron trifluoride and phosphorus trifluoride (67IC1461, 67MI51400). Thietane (210) has been patented as a stabilizer for poly(vinyl chloride) (73USP3767615). 

Dicarbonyl(cyclopentadienyl)(ethyl vinyl ether)1ron tetrafluoroborate,... 

The metallation of 3-methyl-4//-5,6-dihydro-l,2-oxazine has been shown to take place at the methyl group with hindered bases and at the methylene group with unhindered bases (81JA5916). Deprotonation of (753) with lithium dimethylamide at -65 °C followed by reaction with benzyl bromide gave (754) in 85% yield. This product was converted to enone (755) by reaction first with triethyloxonium tetrafluoroborate to produce an oxoiminium salt. The salt was stirred with trimethylamine and the resulting a,/3-unsaturated imine hydrolyzed with wet silica gel to the enone (Scheme 174). The lithiated derivative of (753) serves as a synthon for the unknown a-anion of methyl vinyl ketone. 

New possibilities were reported by Kagan [529], who observed that vinyl sulfoxides could be activated for the Diels-Alder reaction by alkylation into vinyl sulfonium salts. A number of cycloadditions of these salts occurred then under mild conditions and with high stereoselectivities. The results could be particularly striking, as in the case of the low-temperature (-78°C) reaction of ethoxy p-tolyl vinyl sulfonium tetrafluoroborate (2) with cyclopentadiene. Only the endo isomer (3) was formed with a de. higher than 99%. and isolated in a 62% yield after transformation of the sulfonium adduct into a sulfoxide (with inversion at sulfur) by sodium hydroxide. 

To a solution of (S)-(-)-p-tolyl vinyl sulfoxide (5 mmol) in methylene chloride (5 ml) was added triethyloxonium tetrafluoroborate (5 mmol). After 1.5 h with stirring under argon, the salt was precipitated with ether. The solution was cooled to -78°C and the ethereal fraction eliminated by decanting. The residual oily sulfonium salt was washed three times with ether and dried under reduced pressure to give the compound (2) (yield 90%, thermally unstable). 

It has been shown that selective a-vinylation of enolate anions derived from 1,3-dicarbonyl compounds can be achieved by reaction with 4-/-butyl-1 -cyclohcxcnyl-(aryl)iodonium and 1 -cyclopentenyl(aryl)iodonium tetrafluoroborates without competing a-arylation, provided that the alkenyliodonium salt used bears a / -mcthoxyphcnyl, rather than phenyl, group.24... 

With this end in view, phenyldimcthylsilyl tri-n-butylstannane was added under the influence of zero-valent palladium compound with high regioselectivity and in excellent yield to the acetylene 386 to give the metallated olefin 387 (Scheme 56). The vinyl lithium carbanion 388 generated therefrom, was then converted by reaction with cerium(lll) chloride into an equilibrium mixture (1 1) of the cerium salts 389 and 390 respectively. However, the 1,2-addition of 389 to the caibonyl of 391, which in principle would have eventually led to ( )-pretazettine, did not occur due to steric reasons — instead, only deprotonation of 391 was observed. On the other hand, 390 did function as a suitable nucleophile to provide the olefinic product 392. Exposure of 392 to copper(II) triflate induced its transformation via the nine membered enol (Scheme 55) to the requisite C-silyl hydroindole 393. On treatment with tetrafluoroboric acid diethyl ether complex in dichloromethane, compound 393 suffered... 

In a recent series of studies focused on the synthetic utility of alkenyliodo-nium salts, ( )-/J-phenylethenyl(phenyl)- and ( )-l-hexenyl(phenyl)iodonium tetrafluoroborates, 22 and 23, were utilized for alkenylations of a range of soft, anionic nucleophiles (Scheme 45) [128-135]. In all cases but one, alkenylations with 22 occurred with retention of configuration, while alkenylations with 23 occurred with inversion of configuration. Only the dialkyl phosphoroselenolate salts gave mixtures of (Z)- and (fj)-products with 22 [132]. Furthermore, although cuprous iodide was used to catalyze the reactions of 22 and 23 with the phosphorothioate and -dithioate salts, the stereochemical results were the same [131,133]. It was generally assumed that retention was an outcome of the ligandcoupling or addition-elimination pathways, while stereochemical inversion was attributed to the vinylic... 

Plasma polymerized N-vinyl-2-pyrrolidone films were deposited onto a poly(etherurethaneurea). Active sites for the immobilization were obtained via reduction with sodium borohydride followed by activation with l-cyano-4-dimethyl-aminopyridinium tetrafluoroborate. A colorometric activity determination indicated that 2.4 cm2 of modified poly(etherurethaneurea) film had an activity approximately equal to that of 13.4 nM glucose oxidase in 50 mM sodium acetate with a specific activity of 32.0 U/mg at pH 5.1 and room temperature. Using cyclic voltammetry of gold in thin-layer electrochemical cells, the specific activity of 13.4 nM glucose oxidase in 0.2 M aqueous sodium phosphate, pH 5.2, was calculated to be 4.34 U/mg at room temperature. Under the same experimental conditions, qualitative detection of the activity of a modified film was demonstrated by placing it inside the thin-layer cell. 

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