Tropylium fluoroborate

The allenylsilanes are excellent nucleophiles and they can react with a variety of electrophilic species in annulation processes that provide access to diverse products. Allenylsilane 112 (Eq. 13.36) reacts with tropylium fluoroborate 111 to provide azu-lene 113 [35]. The reaction is slow and it is necessary to use an acid scavenger so as to inhibit protiodesilylation by the fluoroboric acid that is generated during the course of the annulation. The excess tropylium salt abstracts a hydride from the reaction intermediate leading to the azulene. There are relatively few direct methods for the synthesis of azulenes. 

Reaction of CF with benzene generates the 7-fluoronorcaradien-7-ly radical (39), which abstracts hydrogen (from added isobutane) and opens to 7-fluorocyclohepta-triene (40). Cycloheptatriene (10) is trapped as tropylium fluoroborate (41) by the addition of BF3 (Eq. 21)P An additional product of CF + benzene is fluorobenzene (42), in which labeling studies demonstrate that the attacking carbon contains the fluorine in 42. The interesting transfer of CH in Eq. 28 is proposed to account for the formation of 42. " ... 

An intermediate cycloheptatetraene can also be trapped in the addition of carbon to benzene itself. When atoms react with benzene-i/e and HBF4 is added, tropylium fluoroborate (41), containing deuterium on the labeled carbon, is observed. This result is consistent with an initial C—D insertion by carbon to give 51- 6, which ring expands to and is trapped by HBF4 (Eq. 37). ... 

Many tropylium salts are coloured although the carbenium ion only absorbs at 217 and 273 nm. The photolysis of colourless tropylium fluoroborate in 5% sulphuric acid with a medium-pressure mercury lamp was studied by van Tamelen et Valence-... 

Tropone. Tropone (2) can be prepared from tropylium fluoroborate (I, 1261) in... 

For regeneration of the hydrocarbon an aqueous solution of tropylium fluoroborate is treated with an aqueous solution of sodium borohydride and tropilidene is collected by ether extraction K. Conrow, Org. Syn., 43,101 (1963)... 

The hydrocarbon is conveniently purified and stored as tropylium fluoroborate, which is indefinitely stable, nonhydroscopic, and nonexplosive. The procedure is as follows. Tropilidene is added to a suspension of phosphorus pentachloride in... 

Saits of nonbenzenoid aronuttic hydrocarbons. Tropylium fluoroborate (3) is the salt of choice for the preparation of substituted tropilidenes because it is indefinitely stable, nonhygroscopic, and nonexplosive. A convenient procedure for its preparation involves reaction of tropilidene (1) with phosphorus pentachloride in carbon tetrachloride to produce a precipitate of the double salt (2). The salt is stirred into... 

Tropylium fluoroborate. A suspension of 100 g. of PCI3 (33% excess) in 800 ml. of carbon tetrachloride is agitated with an efficient stirrer and 0.24 m. of 91%... 

Butyl alcohol Ethylene oxide — Tropylium Fluoroborate 75-83 atm — f... 

To a three-necked flask equipped with a mechanical stirrer, thermometer, gas inlet, and gas outlet device is added 112gm (1.5 mole) of tert-butanol. Then 0.5 gm (0.45 wt%) of tropylium fluoroborate is added and the temperature rises to 75-83°C. Then 132 gm (3.0 mole) of ethylene oxide is added over a 1-hr reaction time. The final product is obtained by neutralizing with sodium hydroxide, filtering the salts, and stripping the resulting liquid under reduced pressure. The unreacted alcohol amounted to only 10%. 

Addition of thiocyanic acid to alkenes is rather interesting in view of the am-bident nature of the thiocyanate ion. Norbornene gives a mixture containing 90% isothiocyanate and 9% thiocyanate (34), suggesting considerable hardness of the cationic carbon. In contrast, addition of HNCS to acrylic esters leads to thiocyanate adducts exclusively. The S end is employed to bond with the P carbon of the unsaturated acyl system. It should be noted that neutralization of tropylium fluoroborate with NaSCN yields cycloheptatrienyl isothiocyanate (35). 

Synthesis of cycloheptatrienes from tropylium fluoroborates Vicarious nucleophilic substitution... 

A soln. of startg. chlorosulfone in DMF added via syringe to a stirred soln. of KOBu-/ in the same solvent at —40° under argon, after 5 min tropylium fluoroborate in DMF added dropwise during ca. 5 min below —40°, and stirred for a further 5 min - chloro(7-cycloheptatrienyl)phenyl(phenylsulfonyl)methane. Y 65%. F.e. and hepta-fulvenes by 1,2-elimination s. S. Ostrowski, M. Makosza, Ann. Chem. 1989, 95-7. 

A soln. of cyclohexanone morpholine enamine in dioxane added to an aq. soln. of tropylium fluoroborate, and stirred 0.5 hr. at room temp. 2-tropylcyclo-... 

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