Triphenylcarbenium tetrafluoroborate

Solubility sol most standard organic solvents reacts with some 

Form Supplied in yellow solid commercially available. Preparative Methods the most convenient procedure involves the reaction of PhsCCl with SUver(I) Tetntfluoroborate in ethanol. The most economical route employs the reaction of Ph3CCl with the anhydrous Tetraftuoroboric Acid-Et20 complex, or PhsCOH with HBF4 in acetic anhydride. Purification recrystallization of commercial samples from a minimal amount of dry MeCN provides material of improved purity, but the recovery is poor.  

Handling, Storage, and Precautions moisture-sensitive and corrosive. Recrystallized reagent can be stored at rt for several months in a desiccator without significant decomposition. This compound is much less light-sensitive than other trityl salts such as the perchlorate.  

Preparation of Aromatic Compounds via Dehydrogenation. Dihydroaromatic compounds are easily converted into the corresponding aromatic compound by treatment with triphenylcarbenium tetrafluoroborate followed by base. Certain a,a-disubstituted dihydroaromatics are converted to the 1,4-dialkylaromatic compounds with rearrangement (eq 1). Nonbenzenoid aromatic systems, e.g. benzazulene or dibenzosesquifulvalene, are readily prepared from their dihydro counterparts. Aromatic cations are also easily prepared by hydride abstraction, for example, tropylium ion (e.g. in the synthesis of heptalene (eq 2)), cyclopropenyl cation, and others, including heterocycUc systems. Some benzylic cations, especially ferrocenyl cations, can also be formed by either hydride abstraction or trityl addition. 

Oxidation by Hydride Abstraction. In the early 1970s, Barton developed a method for the oxidative hydrolysis of ketals to ketones, e.g. in the tetracycline series (eq 3). The same conditions can also be used to hydrolyze thioketals. Acetonides of 

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A, A, A, A -tetramethylethylenediamine trimethyl orthoformate tetrapropylammonium perruthenate tetraphenylporphyrin sulfonated triphenylphosphine triisopropylbenzensulfonyl chloride triphenylcarbenium tetrafluoroborate tetrabutylammonium triphenylmethanethiolate toluenesulfonyl... 

Hydride abstraction of complex 5 using triphenylcarbenium tetrafluoroborate provides the iron complex salt 6a [81]. Similar sequences afford the corresponding 3-methoxy-substituted and 2-methoxy-substituted complex salts 6b and 6c [82,83]. 

However, with triphenylcarbenium-tetrafluoroborate, l.l-dimethoxy-2.6-di-phenyl-4-methyl-X -phosphorin 220 easily splits off a hydride ion to form a resonance-stabilized carbenium-phosphonium-oxonium-ion 221, as Schafer has found The high electron density of the X -phosphorin system, which is in exellent agreement with the theoretical model of Schweig and coworkers (see p. 115), facilitates this interesting reaction. 

Another and still more stabilized carbenium-phosphonium-oxonium-tetra-fluoroborate 225 can be prepared when bis-4.4- (l, l-dimethoxy-2.6-diphenyl-X -phosphorin)-methane 224 is treated with triphenylcarbenium-tetrafluoroborate. 

Isoseleno- and isotellurochromenes 85 can be readily converted to the corresponding 2-benzoseleno- and 2-benzo-telluropyrylium tetrafluoroborates 86 by treatment with triphenylcarbenium tetrafluoroborate (Equation 35) <2002J(P1)606>. An analogous reaction has also been used for the conversion of tellurochromenes 87 to the corresponding 1-benzotelluropyrylium salts 88 (Equation 36) <1999J(P1)1665>. When the ring substituent was methyl or isopropyl, the desired benzotelluropyrylium salts formed but could not be isolated due to elimination of a proton from the substituent. 

A requirement for an a/m-orientation of the hydridic p-C—H and C—metal bonds as in [10] is indicated by the reaction of threo-3-deuterio-2-(trimethylstannyl)butane with triphenylcarbenium tetrafluoroborate in methylene chloride at 24° which yields a mixture of 3-deuterio-l -butene, /ra v-2-deuterio-2-butene, and undeuteriated c/.v-2-butene as the major product (Hannon and Traylor, 1981). Comparison of the product distributions for the protio- and deuterio-stannanes yields primary and secondary isotope effects of 3.7 and 1.1 respectively. These reactions appear to avoid the complications of adduct formation between the triarylcarbenium salt and the hydride donor, but the preferential formation of the cw-2-butenes is not fully explained. The requirement for the anti-orientation is also shown by the relatively low hydride-donating properties of tris[(triphenylstannyl)methyl-methane (Ducharme et ai, 1984a) which adopts a C3-conformation with the P-C—H gauche to all three C—Sn bonds. In contrast, 1,3,5-triphenyl-2,4,6-trithia-1,3,5-tristannyladamantane, in which anti-orientations with respect to the bridgehead C—H bond are locked, shows high reactivity (Ducharme et al., 1984b). 

The contrasting behaviour of the tricyclic orthoamides [44] and [45] towards triphenylcarbenium tetrafluoroborate has also been rationalized in terms of the necessity of adduct formation in the removal of the tertiary hydrogen (Atkins, 1980 Erhardt and Wuest, 1980). The dominant con-former of [44] has C3v symmetry, so that the central C—H is antiperi-planar with respect to all three nitrogen lone pairs. This hydrogen shows... 

The treatment of 2//-l,3-ditclluroles in acetonitrile at 30° with an equimolar amount of triphenylcarbenium tetrafluoroborate produced substances, the NMR spectra of which suggested that they were 1,2-ditelluroIium salts2. 

H-1,3-Ditelluroles treated in acetonitrile with triphenylcarbenium tetrafluoroborate were converted to 1,3-ditellurolium cations at — 30°. These cations rearranged to 1,2-ditcllurolium cations at + 30°2 (p. 796). 

Weigh 0.10 g of 4W-pyran hemispherand 16b in the flask. Subsequently add 2 mL of ethylene glycol dimethyl ether and 0.10 g of triphenylcarbenium tetrafluoroborate. 

The final step of a synthesis of the alkaloid Monocrotaline [Scheme 3.94] required liberation of a hindered 1,2-diol encased in the methylene acetal 941.173 The task was accomplished by a hydride abstraction reaction using triphenyicar-benium tetrafluoroborate to give an intermediate of unknown structure whose hydrolysis afforded Monocrotaline in 86% yield. Triphenylcarbenium tetrafluoroborate can also be used to deprotect dioxolane derivatives of ketones174 and benzylidene derivatives.1755... 

Methyl rheniumpentacarbonyl has been subjected to three tetrafluoro-boranation studies, all by Beck and co-workers (20,162,163). The first study (162) involved treating the tetrafluoroborate derivative (formed by reaction of [Re(CH3)(CO)5] with triphenylcarbenium tetrafluoroborate) with a variety of cr and v donors, L, forming the salts [Re(L)(CO)s] BF4 [Eq. (51)]. The second study involved the formation of binuclear rhenium compounds (20) [Eq. (52)]. The third study used the tetrafluoroboranation reactions as a route to a polynuclear rhenium compound (163) [Eq. (53)]. 

If 1,3-ditelluroles, with at least one hydrogen present on the ring, are treated in MeCN with triphenylcarbenium tetrafluoroborate, the H NMR spectra of the solution show the formation of... 

The synthesis of 2,4,6-triaryl-l,3,5-thiadiazinium tetrafluoroborates (e.g. (94)) by abstraction of hydride ion from 2,4,6-triaryl-4//-l,3,5-thiadiazines (e.g. (93)) with triphenylcarbenium tetrafluoroborate has been reported (Equation (3)) <73BCJ3902, 80BCJ3369, 81JAP(K)5657778, 81JAP(K)5657779>. 

Olah et al. (1992) studied the reaction of triphenylcarbenium tetrafluoroborate (10 mmol) with diphenyldiazomethane in dry dichloromethane hoping to detect the 1,1,2,2,2-pentaphenylethyl cation (9.25). The reaction yielded, however, tetraphenyl-ethene (79%) and a small amount (< 0.2%) pentaphenylethane. Using perdeuterated triphenylcarbenium salt or C-enriched diphenyldiazomethane, the authors demonstrate, by analysis of the labeled products, that the results are consistent with the mechanism (9-17), i.e., with the 1,1,2,2,2-pentaphenylethyl cation as steady-state intermediate, which is expected to undergo 1,2-phenyl migration via a phenonium ion and subsequent phenyl group scrambling. 

In a synthesis of the pyrrolizidine alkaloid Integenimine, a methylthiomethyl ether protecting group was removed in the final step by hydride abstraction using triphenylcarbenium tetrafluoroborate (Scheme 4.321]. ... 

The synthesis of 7-oxygenated carbazoles via the iron-mediated route requires the 2-methoxy-substituted iron complex salt 52 (Scheme 14). Complexation of the methoxycyclohexadienes 47 and 48 with pentacarbonyliron in the presence of catalytic amounts of l-(p-anisyl)-4-phenyl-l-azabuta-1,3-diene affords a mixture of the regioisomeric 1 -methoxy- and 2-methoxy-ri -cyclohexadieneiron complexes 49 and 50 [77, 78, 84]. Hydride abstraction by triphenylcarbenium tetrafluoroborate provides a mixture of regioisomeric ri -cyclohexadienyUron complexes 51 and 52. Separation of the 1-methoxy- and 2-methoxy-substituted complex salts 51 and 52 can be achieved by selective hydrolysis of 51 to the cyclohexadieno-ne—tricarbonyliron complex 53 [74]. 

A solution of 1.98g of triphenylcarbenium tetrafluoroborate in nitromethane was added to a nitromethane solution of the mixed... 

Bryce et al. (1984) have reported the preparation of a highly conjugated bisbenzothiazoline (124) by the reaction of dimethyl cyclohexa-l,3-diene-l,4-diacetate (121) with 2-(methylamino)benzenethiol (122) in the presence of triphenylcarbenium tetrafluoroborate and the subsequent treatment of the resultant bisbenzothiazolium tetrafluoroborate (129) with triethylamine at 20 °C (Scheme-35) (Biyce et al. 1984). 

Boron Trifluoride Etherate in the presence of Thioanisole Magnesium Bromide in the presence of butanethiol, Triphenylcarbenium Tetrafluoroborate, and Lithium Tetrafluoroborate are also useful for eleavage of the MOM group. The action of lithium tetrafluoroborate is unique (eq 7) and the meehanism for cleavage is not well understood. 

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