Tris- cyclopropenylium

Tris(t r/-butylsulfanyl)cyclopropenylium perchlorate (17) behaves as a bi-electrophile towards benzene-1,2-diamines, yielding 3, 4-bis(tm-butylsulfanyl)-17/-l,5-benzodiazepines 18.267... 

Bordwell, 1988), contributed to the successful isolation of the first hydrocarbon salt [l 2 ], when it was combined with Agranat s cation, tris(3-guaiazulenyl)cyclopropenylium ion [1" ] (Agranat and Aharon-Shalom, 1976). 

Unlike such unstable intermediates, the first, rare example of reversible dissociation of a carbon-carbon a bond into a stable carbocation and carbanion was reported for a nitro-dicyano compound (20) prepared from trimethyl- and triphenyl-cyclopropenylium tetrafluoroborate ([4" ]BF4 and [5 JBFJ) with the potassium salt of p-substituted-phenylmalononitrile anions (Arnett et al., 1983 Troughton et al., 1984 Arnett and Molter, 1985). Other ionically dissociative malononitrile derivatives have been prepared from such carbocations as the tropylium [S ] (Arnett and Troughton, 1983) and the tris(p-methoxyphenyl)methylium [93 j (Arnett and Troughton, 1983) ions. 

In view of the ease of dissociation of the a bond into resonance-stabilized hydrocarbon ions, it is expected that an authentic hydrocarbon salt could be isolated from an extraordinarily stable cation and anion. The first synthesis of a salt composed solely of carbon and hydrogen was achieved on the combination of tris(3-guaiazulenyl)cyclopropenylium ion [1" ] and tris(7//-dibenzo[c,g]fluorenylidenemethyl)methanide ion [2 ] (Okamoto et al., 1985). 

A variety of functionalized [3]radialenes have been prepared starting from the appropriately substituted cyclopropanes or cyclopropenes. West and Zecher have pioneered the chemistry of [3]radialenes with quinoid substituents. The general strategy of this synthesis is outlined in Scheme 513. A tris(4-hydroxyphenyl)cyclopropenylium... 

TRI- ferf-BUTYLCYCLOPROPENYL FLUOROBORATE (Cyclopropenylium, tri- er/-butyl tetrafluoroborate)... 

The pKR+ value for the parent tri(l-azulenyl)methyl cation (2a+) is 11.3. Hydrocarbon-based carbocations, which comprise only of carbon and hydrogen, are generally very reactive species. Some extremely stable hydrocarbon carbocations, which exist even under basic conditions, were reported in the literature (5). However, most of these examples are cyclic cations, such as cyclopropenylium or tropylium ions (Figure 8). The tropylium ion 8+ annelated to three bicyclo[2.2.2]octane units is one of the most stable hydrocarbon-based carbocation ever reported (9). 

Die Wahl des Losungsmittels bestimmt, welches Produkt bei der Cyclisierung von 1,2-Diamino-benzol mit Tris-[tert.-butylthio]-cyclopropenylium-perchlorat gebildet wird. In Methanol ent-steht 2-(1,2-Bis-[tert.-butylthio]-ethenyl)-benzimidazol (77%, tiber ein Allyl-Kation), im apro-tischen Dimethylformamid in einer inneren Michael-Addition 3,4-Bis-[tert.-butylthid -IH-l, 5-benzodiazepin (63% roh 100%)189. 

X-ray structure analysis of the tris(trimethylsilyl)cyclopropenylium cation... 

The tris(trimethylsilyl)cyclopropenylium hexachloroantimonate 300 SbCI() forms crystals which are stable at room temperature121. 

C67H , which consists of the tri(cyclopropyl)cyclopropenylium cation and Kuhn s anion, is completely ionized in the solid and in DMSO solution. However, in chloroform, tetrachloromethane, and benzene solutions at room temperature, a covalent hydrocarbon is formed from the two ions. Surprisingly, cooling the chloroform solution to -78 °C or evaporation of the solvent regenerates the original green hydrocarbon salt. 

Another hydrocarbon salt, composed of the tri(cyclopropyl)cyclopropenylium cation and Kuhn s anion, which can exist in all three types of elementary organic species i.e. as an ionic, radical, and covalent compound) in a solution equilibrium, depending on the solvent, has already been mentioned in Section 2.6 [292]. 

Cyclopropenylium Tris-[methylthio]-(Salze) V/2c, 7ff. E17d, 3092 (Cl4—cyclopropen + R—SH), 3094f. (Br4 —cyclopropen + R2S2)... 

Cyclopropenylium Tris-[methyltellu-ro]- (tribromid) V/2c, 9 E17d, 3096 (Cl4 —cyclopropen + R3Te2)... 

Cyclopentenylium 1,2,3-Tris-[dimethylamino]- E17d, 3166 (Cyclopropenylium + Ethen)... 

The base peaks in the 70 eV electron impact mass spectra of 3,3-dimethylcyclopro-pene (223) , 3-substituted 1,2-diphenylcyclopropenes (224), 3-thiocyanato-1,2,3-triphenylcyclopropene (227) and tri-t-butylcyclopropenyl azide (229) just to mention a few examples, are often found to correspond to the loss of the (3)-substituent, thereby generating the substituted cyclopropenylium ions 215, 225, 226, 228 and 230, respectively (Scheme 33). It should be mentioned, however, that there exists at least one report describing the complete absence of cyclopropenyhum-type ions in 70 eV mass spectra of 1,2-dialkyl-substituted cyclopropenes. The reported spectra indicate that allylic cleavage seems to be operative, although no further experimental results are known which would lend support to such a suggestion. 

Oxidation of l,2,3-tri-tf>/-Cbutylcyclopropene (2) with 3-chloroperoxybenzoic acid in dichlo-romethane at room temperature gave di-/err-butylacetylene in a reaction shown to involve hydrogen abstraction from C3 and trapping of the cyclopropenylium ion so produced by per-oxybenzoate ion to give 3. ... 

To a solution of tris(dimcthylamino)cyclopropenylium perchlorate (300 mg. 1.12 mmol) in MeOH (10 mL) was added 6.5 M aq KOH (10 mL). The mixture was allowed to stand for 2d at 20 C. The mixture was diluted with H2O, and extracted with CHjClj (50 mL). After removal of the solvent, the residue was recrystallized (El,0) to afford the ketone as extremely hygroscopic needles yield 114 mg (73%). 

To a solution of tris(dimethylamino)cyclopropenylium perchlorate (2.68 g, 10 mmol) in MeOH (150 mL) was added dropwise, with stirring at 0 C, 0.58 M NaSH in EtOH (150 mL). The mixture was stirred at 20 C for 20 h. To this was added HjO (200 mL). The product was extracted with benzene. After evaporation of the solvent, the residue was triturated (EtjO) to give the thione, which was purified by sublimation under reduced pressure yield 1.30 g (83%) mp 145 C. 

Reaction of tris(tert-butylsulfanyl)cyclopropenylium salt with anhydrous sodium hydrogen carbonate in refluxing ethyl acetate gave the thione 5 in 90% yield. This reaction has not been used for the preparation of other cyclopropenethiones. 

Treatment of tris(2-trimethylsilylethylsulfanyl)cyclopropenylium fluoroborate with zinc powder in acetonitrile resulted in the formation of the thione 6a in 54% yield.Likewise 2,3-bis (ter -butylsulfanyl)cyclopropenethione (6b) was formed from tris(to7-butylsulfanyl)cyclo-propenylium fluoroborate. No other examples have been reported. 

A mixture of tris(ethylsulfanyl)cyclopropenylium perchlorate (2.23 g, 7 mmol) and benzoyl(pyridyl)amide (1,01 g, 5.1 mmol) in freshly distilled DMSO (30 mL) was stirred at 80 C for 8h under N. After the mixture had been allowed to stand for 12 h, the solvent was removed under reduced pressure. The residue was purified by column chromatography (silica gel) to give the urea yield 0.78 g (60%). 

Reaction of tris(tef-f-butylsulfanyl)cyclopropenylium perchlorate (0.81 g, 2 mmol) and ethoxycarbonyl(py-ridyl)amide (0.33 g, 2 mmol) was carried out in dry THF (30 mL) as described in method A. After removal of the solvent, the residue was extracted with benzene. The benzene solution was concentrated to dryness, and the resulting residue extracted with EtjO to give the urea yield 0.15 g (31%). 

The reaction of tris(4-to- -butylphcnylsulfanyl)cyclopropenylium perchlorate (1.77 g, 2.8 mmol) and acetyl(dimethylsulfanyl)amide (1.00 g, 8.4 mmol) in CHCI3 (30 mL) was carried out at 20 C as described in method A. After removal of the solvent, the residue was dissolved in MeCN and extracted with petroleum ether. Evaporation of the petroleum ether solution, and recrystallization (CHClj/EtjO) afforded the urea yield 0.72 g (73%). 

Treatment of tris(terr-butylsulfanyl)cyclopropenylium fluoroborate with cyanamide or p-tolu-enesulfonamide in the presence of 2,4,6-trimethylpyridine produced 2,3-bis(alkylsulfanyl)cyclo-propenimines 7. ... 

To a stirred solution of tris(ter/-butylsulfanyl)cyclopropenylium fluoroborate (2.0 g, 5.1 mmol) and cyan-amide (0.22 g, 5.1 mmol) in CH Clj (50 mL) was added dropwise 2,4,6-trimethylpyridine (0.93 g, 7.7 mmol) at 20 C. After I h stirring, the solvent was removed. The residue was purified by column chromatography (silica gel, CHClj). Recrystallization (Et20/hexane) afforded the imine yield l.Og (78%) mp 112°C. 

The reaction of tetrachlorocyclopropene (3) with thiols in the presence of silver(I) tetrafluoro-borate in acetonitrile afforded the tris(alkylsulfanyl)cyclopropenylium tetrafluoroborates... 

I,2,3-Tris(/ Tf-butylsulfanyl)cyclopropenylium Tetrafluoroborate (4, R = r-Bn) Typical Procedure - ... 

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