Trityl tetrafluoroborate

Attempts to prepare 2-aminoazepinium cations by the action of trityl tetrafluoroborate on 3//-azepin-2-amines have failed,64 as have attempts to Ar-methylate 2,5,7-trimethyl-3/f-azepine with an excess of iodomcthanc in a scaled tube at 100°C for seven hours.77 In contrast, the unstable Ar,Ar-dialkyl-6-(methylsulfanyl)-3//-azepin-2-amines, e. g. 1, with trityl tetrafluoroborate, or the corresponding nitrosonium salts, yield their tetrafluoroborate salts, e.g. 2s4 (see also Section 3.1.1.5.4.). 

The C6 position of a V,./V-dialkyl-3//-azepin-2-amine, e.g. 1, displays remarkable reactivity towards electrophilic substitution, and with dimethyl(methylsulfanyl)sulfonium tetrafluorobor-ate undergoes methylsulfanylation and quaternization to yield 6-(methylsulfanyl)-3//-azepin-ium tetrafluoroborates, e.g. 2, identical to those obtained by quaternization of the free bases with trityl tetrafluoroborate.64 Basification of the salts with potassium carbonate yields the free bases, e.g. 3, which decompose during distillation or on exposure to air. 

Attempts to prepare 2-aminoazepinium salts by the action of trityl tetrafluoroborate on azepin-2-amines, e.g. 18, resulted in ring contraction to stable 2-azabicyclo[4.1.0]hepta-2.4-dienium salts, e.g. 3-(pyrrolidin-l-yl)-7-trityl-2-azabicyclo[4.1,0]hcpta-2,4-dicnium tetrafluoroborate (19), the valence isomers of 7-(dialkylamino)-3-trityl-3//-azepinium tetrafluoroborates 64 with Meerwein s reagent the 2-ethyl derivative (77%) is formed. 

The agents used for oxidative aromatization of various thiopyrans were air-dioxygen (81KFZ38 83KGS1689 91KGS181), trityl tetrafluoroborate (81CC1143 85CL1119), 3,4-di-(/-butyl)-l,2-benzoquinone (DTBQ)... 

Bis(ethylenediamine)gold(III) chloride reacts with /3-diketonates in aqueous base via Schiff base condensation to form complexes of gold(III) with a 14-membered macrocyclic tetraaza ligand such as (292).1711-1713 The X-ray structure showed the cation to be nearly planar. Delocalization of -electrons within the six-membered /3-diketonate rings was indicated by the observed pattern of C—C and C—N distances. Open-chain tetraaza ligand complexes in which condensation of only one /3-diketonate has occurred, can be isolated as intermediates in this reaction. They may be used for further condensation with a different /3-diketonate. Oxidation of this complex with trityl tetrafluoroborate introduces a double bond in position C2C3.1712,1714... 

Organosilicon hydride reductions of preformed stable carbocations such as triphenylmethyl (trityl) tetrafluoroborate and hexafluoroantimonate salts are rapid... 

Alkene synthesis. A regio- and stereoselective alkene synthesis is formulated in equations (I)—(III). The first step involves formation of the alkyliron complex 1. Treatment of 1 with trityl tetrafluoroborate abstracts a -hydrogen to give a cationic iron complex 2. Liberation of the free alkene is effected by Nal in acetone. This sequence is useful because 1- and 2-alkyliron complexes (1) are converted into 1-alkcncs exclusively 3-alkyliron complexes are converted exclusively into the less stable (Z)-2-alkenes. The paper includes some 20 examples of alkenes prepared in this way. 

Like tetraalkylsilanes, the silacyclohexanes are stable to most electrophiles and nucleophiles. A notable exception is trityl tetrafluoroborate (Scheme 218) (74jOM(81)41). 

Treatment of 2-(rm-butylthio)-116-benzyl-3,4-diphenyl-2,6,7,116-tetrahydro[l,3]thiazino[2,3-a]isoquinoline with trityl tetrafluoroborate in acetic anhydride at 0°C gave 116-benzyl-3,4-diphenyl-6,7-dihydro-... 

Interestingly it is also possible to form a stable silicon-fluorine bond by treatment of a methoxysilole with boron-tnfluonde etherate or of a silole with trityl tetrafluoroborate [106] The resultant fluorosilane is also a building block for further transformations of the silole (equation 84)... 

The parent ion 5 and its naphtho[6] analogue have been generated by treatment of 1 and 11, respectively, with trityl tetrafluoroborate. The cations so formed are captured by water and the final product of reaction is the ring opened aryl aldehyde (equation 24)230 231. Kinetic measurements have shown230 that abstraction of hydride ion from 1 is first order and displays a deuterium isotope effect of 6.5. To the best of the author s knowledge, the isolation and spectroscopic characterization of an unsubstituted cycloproparenyl cation has yet to be achieved. 

Keto sulfides.1 In the presence of trityl tetrafluoroborate, silyl enol ethers react with thioacetals or -ketals to give 7-keto sulfides in 75-95% yield (equation I). The same products can be obtained directly from ketones and thioacetals by in... 

Trialkylaluminums, 204 Trichloroisopropoxytitanium, 300 Triisobutylaluminum, 205 Trimethylaluminum, 205 Trityl perchlorate, 339 Trityl tetrafluoroborate, 301 Zinc bromide, 349 Zinc chloride, 44, 108, 181, 190, 349 Zinc iodide, 88, 112, 280, 349, 350 Zirconium(IV) acetylacetonate, 351 Zirconium(IV) chloride, 16 Zirconium(IV) isopropoxide, 311 Other Organic and Inorganic Acids Acetic acid, 45 Benzoic acid, 312 Camphor-10-sulfonic acid, 62, 64 Formic acid, 137... 

With methyl-substituted cyclohexadienes, very little selectivity is observed during the preparation of the complexes and the hydride abstraction reaction. Dihydrotoluene, on heating with pentacaibonyliron, gives a mixture of complexes (37) and (38 Scheme 4). These cannot be easily separated using standard chromatographic procedures, and little is known about hydride abstraction from the individual complexes. Treatment of the equimolar mixture with trityl tetrafluoroborate gives a mixture of all three possible products (39-41 Scheme 4). 

Triphenylmethyl (trityl) tetrafluoroborate, on the other hand, is sp2 hybridized but it is also extremely reactive toward electron donors. The acceptor orbital of the trityl cation is an unfilled 2p atomic orbital on the charged carbon. These carbon electrophiles are isolable compounds, but they are extremely reactive with any sort of electron donor (H2O vapor is a common culprit). 

The application of tritylpyridinium tetrafluoroborate, easily obtained from trityl tetrafluoroborate and pyridine, presents definitive advantages [319, 320] over the classical procedure discussed in the previous section. Acetonitrile solvent simplifies the workup procedure, the substantially shorter reaction times enable the use of only a slight excess of the reagent. Preferential tritylation of the primary hydroxyl group in carbohydrates is especially convenient with this method. 

A combination of trityl tetrafluoroborate or perchlorate with 2,4,6-tri(/err-butyl)-pyridine instead of pyridine enables an almost quantitative tritylation of the secondary hydroxyl group in l,2 5,6-di-0-isopropylidene-a-D-glucofuranose in 10 min at room temperature [321]. The more readily available 2,6-di(/m-butyl)-4-methylpyridine was used [322] in combination with trityl perchlorate for the selective tritylation of methyl 2,6-di-0-acetyl-a-D-galactopyranoside at the equatorial OH-3. Combination... 

Sodium azide can react with 1,3-benzodithiolylium tetrafluoroborate (32) in acetonitrile to form the azide (38) which on treatment with trityl tetrafluoroborate yields trityl azide and (32) (80JOC2024). The last step of this reaction does not lead to the expected 2-azido-l,3-benzodithiolylium salt. 

Alkylthio-l,3-dithioles (190) react with trityl tetrafluoroborate in acetonitrile to produce the 1,3-dithiolylium salts (54) in high yields (80AHC(27)15l). 

Oxidation of the 1,2,4-dithiazoline (36) to the cation (34) with trityl tetrafluoroborate (74AP828) is an example of electrophilic attack at ring hydrogen. Nucleophilic attack with... 

The intermediate (VII) (1.48 g., 2.0 mmoles) is dissolved in methylene chloride (50 ml.), and trityl tetrafluoroborate (660 mg., 2.0 mmoles) is added. The clear yellow solution is allowed to stand for 5 minutes then ether (200 ml.) is added. This precipitates an oily white solid. The mixture is allowed to stand until the supernatant liquid is clear (ca. 1.5 hours). The supernatant is then poured off and the solid clinging to the walls of the flask is washed with ether (three times with 50 ml.). It is then dried in a stream of nitrogen and recrystallized twice by dissolving in methylene chloride (ca. 50 ml.) and precipitating with ether (ca. 200 ml.). This gives the product as a white solid. Yield is 1.07 g. (73%).t Anal. Calcd. for C26H27-AsBClF4Pt C, 42.7 H, 3.7 As, 10.2. Found C, 42.5 H, 3.6 As, 10.0. 

The tricarbonyliron-coordinated cyclohexadienylium salts are readily available on a large scale by azadiene-catalyzed complexation of the corresponding cyclo-hexadienes with pentacarbonyliron [23] and subsequent hydride abstraction using trityl tetrafluoroborate [24]. Alkylation of methyl lithioacetate with the iron complex... 

In the dosing stages of a synthesis of Mitomycin derivative FR-900482, a densely functionalised intermediate had to be shorn of its robust MOM protector [Scheme 4.250].46S The task was accomplished with trityl tetrafluoroborate under conditions devised some years ago by Kishi and co-workers.466 Lithium tetrafluoroborate in refluxing aqueous acetonitrile has been successfully deployed in the deprotection of a MOM ether in the presence of a benzyl ether [Scheme 4 2511 467... 

In Schemes 8.204 and 8,205 above we showed that tritylamines can be generated by reductive amination and N-alkylation of trityiamine. However, N-alkyla-tion of amines by triphenylmethyl chloride (mp 110-112 °C) or triphenylmethyl bromide (mp 152-154 °C) in an aprotic solvent such as chloroform or chloro-form-DMF mixtures together with a base such as triethylamine is the most common method for introduting the trityl group [Scheme 8,212]434 4,4 -Dimethoxy-trityl tetrafluoroborate and 4i4, 4"-trimethoxytrityl tetrafluoroborate are also... 

Regioselective oxidation of 2- and 4-alkyl-l,4-hutanediols. 2,2-Disubstituted 1,4-butanediols (1) are oxidized by this combination -.electively to the 7-butyrolactones 2. Cobalt(II) alkanoates and trityl tetrafluoroborate show comparable selectivity. 

CyclodehydrogeruUion chromenes. Reaction of o-(3,3-dimethylallyl)phenols with trityl tetrafluoroborate results in dehydrogenation and cyclization to chromenes. DDQ has usually been used for this purpose. 

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