Tropylium tetrafluoroborate

Irradiation of the sodium salt 517 in a solution of maleonitrile in THF gave a 30% yield of the as-spiro[2.6]nonatrienedicarbonitrile 524 (Scheme 6.106). Analogously, fumaronitrile led to the trans-diastereomer 525 exclusively in 29% yield [193b], which was also obtained from (trimethylsilyl)tropylium tetrafluoroborate (519) as precursor of 5 [208]. The interception of 5 by dimethyl fumarate succeeded by generating 5 from 517 by either photolysis [193] or thermolysis [193, 194] and from 519 [208] and afforded the dimethyl trans-dicarboxylate 526 in yields of 50, 40 and 42%, respectively. Liberation of 5 in the presence of dimethyl maleate led also to 526 [194, 214], In this reaction, the isomerization of dimethyl maleate to fumarate could have interfered and hence pretended the loss of the stereochemical information, since... 

Dicyanoheptafulvene 2,4,6-Cycloheptatriene-A1 -malononitrile (8) Propanedinitrile, 2,4,6-cycloheptatrien-1-ylidene- (9) (2860-54-0) Cycloheptatrienylium tetrafluoroborate Aldrich Tropylium tetrafluoroborate Cycloheptatrienylium, tetrafluoroborate (1-) (8,9) (27081-10-3) Bromomalononitrile, Malononitrile, bromo- (8) Propanedinitrile, bromo- (8) (1885-22-9)... 

CYCLOHEPTATRIENYLIUM TETRAFLUOROBORATE Aldrich TROPYLIUM TETRAFLUOROBORATE CYCLOHEPTATRIENYLIUM, TETRAFLUOROBORATE (1-) (27081-10-3), 75, 210... 

Pyridine, purified by distillation immediately before use must be anhydrous. Cycloheptatrienylium (tropylium) tetrafluoroborate, 1, was prepared by the method of Conrow2 and its purity was at least 99%. Aldrich Chemical Company, Inc., also provides 1. 

The same approach allows preparation of various pyrylium carboranes from the corresponding 4/f-pyran carboranes 174a,b and 175b by the action of acetyl perchlorate,245 perchloric acid,244 and triarylamine radical cation salts,244,245 as well as electrochemically.243 The oxidation of condensed 4H-pyran 345 with trityl perchlorate, 2,3,5,6-tetra-substituted 4f/-pyrans 431 and 153 with tropylium tetrafluoroborate or 153 with heterocyclic salt 393 led to useful preparations of pyrylium salts 394,330 395a,359 and 395b,360 respectively. 

Azulenes.1 In the presence of this polymer as an acid scavenger, tropylium tetrafluoroborate undergoes [3 +2]cyclization with simple allenylsilanes to form azulenes. Trimethoxymethylsilane is the preferred scavenger in the case of higher substituted allenes. 

Many other lithium phenolates can be similarly oxidized. Cycloheptatriene and 14c, suspended in ether, give the tropylium-tetrafluoroborate and the phenol of 14c. 

Analogously, fragmentation to form the aromatic tropylium ion (pKR- = +4.76) [33] is observed when 43 (R—H) is treated with perchloric acid [117]. To demonstrate the counterion effect discussed above, we combined tropylium tetrafluoroborate (44BF4 ) with isobutene in methanol and isolated 43 (R = CH3) in 45% yield [118],... 

Oxidation. Reaction of tropylium tetrafluoroborate (1) with DMSO at 55° (4 hours) results in a product (a) that is converted to tropone (2) on addition of water and chloroform. 

The cation possesses a more favourable geometry than 1,6-methano-[10]annulene, being able to incorporate the 10 -system into a more planar structure. It is evidently more stable than the tropylium ion, as it can be formed from its neutral hydrocarbon precursor 57 by a hydride-transfer reaction with tropylium tetrafluoroborate 136>. The anion, on the other hand, involves substantial steric strain and is not as planar as either the cation or the neutral bridged [lOJannulene. Whereas formation of the cation from 57 was seen to be most favourable, the anion precursor 58 is much less acidic than cyclopentadiene, although in the presence of... 

Tropylium tetrafluoroborate See Cycloheptatrienylium tetrafluoroborate, 75, 210 Tryptones (Bacteriological). See Peptones, Bacteriological (73049-73-7 ), 76, 80... 

Tricarbonyl(2-5-fj-l/f-azepine)iron reacts with tropylium tetrafluoroborate to give a derivative which after decomplexation with trimethylamine oxide, yields 3-(2,4,6-cycloheptatrienyl)-3/f-azep-... 

Reductive dimerization. Bitropyl (2) can be prepared in high yield by reaction of tropylium tetrafluoroborate (1) with TiCls or VCI2 in aqueous THF. The only other satisfactory reagent for such a reduction is zinc dust (tropylium bromide -> bitropyl, 97%, yield). ... 

Many tropylium salts having colourless anions are themselves colourless but the bromide and iodide are, respectively, yellow and red. The colour is due to long tailing into the visible region and has been attributed to charge-transfer complex formation [16,19,40]. On addition of benzenoid hydrocarbons to solutions of tropylium tetrafluoroborate or perchorate new absorption bands appear, which have been attributed to the formation of charge-transfer complexes with the hydrocarbons [45]. 

Improved syntheses of bitropyl and sym-tetrabenzobitropyl have been reported whereby tropylium tetrafluoroborate and dibenzotropylium tetrafluoroborate, respectively, are coupled using vanadium(ii) chloride or titanium(iii) chloride. Trimethylene-8,8-dithiaheptafulvene (125), an electron-rich heptafulvene, has been prepared from the adduct of 2-lithio-l,3-dithian and tropylium tetrafluoroborate, and its reactions with reactive dienophiles have been examined. " The sym-dibenzo analogue of (125) has also been described.anti-[2,2] (2,6)-Azulenophane has been prepared by the dimerization of (126). ... 

Aspects of the chemistry of 2-hydroxycyclo-octa-2,4,6-trienone have been studied. Addition of bromine gives the 2,3-adduct, which if passed immediately through a column of fluorsil eliminates HBr to give 3-bromo-2-hydroxycyclo-octa-2,4,6-trienone, but which if left at room temperature for several hours gives 7-bromo-cyclo-octa-3,5-diene-l,2-dione after chromatography. Other reactions of 2-hydroxy-cyclo-octa-2,4,6-trienone which have been reported include alkylation and acylation, treatment with tropylium tetrafluoroborate to give a mixture of (244 = tropyl,... 

Synthesis of Azulenes. Reaction of tropylium cations with allenylsilanes produces substituted azulenes. Typically, commercially available tropylium tetrafluoroborate (2 equiv) is ert5)loyed. The second equivalent dehydrogenates the dihydroazu-lene intermediate to produce the aromatic product. Poly(4-vinyl-P3Tidine) (poly (4-VP)) or methyltrimethoxysilane is used to scavenge the HBF4 produced in the reaction. 

Monoreaction of H-T2-H 2 with tropylium tetrafluoroborate gave in 40% yield the monosubstituted bithiophene 401 which was isomerized to the corresponding 4H-derivative 402. Oxidative homo-coupling of lithiated bithiophene 402 with CuCl2 gave the disubstituted quaterthiophene 403 in a moderate yield (27%). Following hydride... 

Carbonyl Compounds. A convenient synthesis of tropone (52%) involves treatment of tropylium tetrafluoroborate with sodium azide to produce tropylium azide, followed by reaction with basic alumina. ... 

Similarly, hydride abstraction from (OsH(CD)2(tl5-Cp)) by tropylium tetrafluoroborate in dichloromethane at 25 C for six days gives the complex, [Os(CO)2(l,2- n2-C7H8)(Tl5-Cp)]IBF4Lin 80% yield.77... 

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