Tetrafluoroborate triethyloxonium reaction

Neutral tertiary and secondary amides react with very reactive alkylating agents, such as triethyloxonium tetrafluoroborate, to give O-alkylation.63 The same reaction occurs, but more slowly, with tosylates and dimethyl sulfate. Neutralization of the resulting salt provides iminoethers. 

These reactions involve addition of the diazo ester to an adduct of the carbonyl compound and the Lewis acid. Elimination of nitrogen then triggers migration. Triethyloxonium tetrafluoroborate also effects ring expansion of cyclic ketones by ethyl diazoacetate.83... 

A cyclized version, xilobam (S), is synthesized from ji-methylpyrrolidone by conversion to the imine (]) by sequential reaction with triethyloxonium tetrafluoroborate and then anhydrous ammonia. When this is reacted with 2,6-dimethyl-phenyl i socyanate, the centrally acting muscle relaxant xilobam (8) is formed. ... 

One of the major advantages of oxonium salts is that alkylations can be effected under reaction conditions that are generally much milder than those necessary with the more conventional alkyl halides or sulfonates. Triethyloxonium tetrafluoroborate, for example, has usually been employed at room temperature in dichloromethane or dichloroethane solution. Occasionally chloroform16-22 or no solvent at all4-20 is used. Difficult alkylations can be effected in refluxing dichloroethane.29 30 The less soluble trimethyloxonium tetrafluoroborate has been used as a suspension in dichloromethane or dichloroethane, or as a solution in nitromethane or liquid sulfur dioxide. Reports of alkylations in water23 and trifluoroacetic acid21 have also appeared. Direct fusion with trimethyloxonium tetrafluoroborate has succeeded in cases where other conditions have failed.25-30... 

Treatment of meso-ionic l,2,3,4-oxatriazole-5-thiones (286) (Section VII, I, 3) with boiling ethanoUc ammonia yields the isomers 297. These belong to a new class of meso-ionic heterocycle, which by O-alkylation with triethyloxonium tetrafluoroborate 3rield the salts 298, These are useful intermediates for the sjmthesis of a number of novel types of meso-ionic 1,2,3,4-thiatriazoles (299, 300, and 301). The l,2,3,4-thiatriazol-5-ones (297) have dipole moments in accord with their meso-ionic formulation. They are remarkably stable to acidic hydrolysis, and 1,3-dipolar cycloaddition reactions have not been observed alkaline hydrolysis yields aryl azides. 

The unsymmetrical 3,6-dialkoxy-2,5-dihydropyrazines are prepared via the jV-carboxyanhy-drides of the particular amino acid (e.g., 7) and subsequent reaction with the methyl ester of glycine or alanine to give the corresponding cyclodipeptides (e.g., 8). These hexahydrodioxopy-razines are converted to the 2,5-dialkoxy-3,6-dihydropyrazines by alkylation using Meerwein salts, such as trimethyloxonium tetrafluoroborate or triethyloxonium tetrafluoroborate n lb. 

Triethyloxonium tetrafluoroborate in dichloromethane was used to convert the trimethylsilyl ether of a dioxopyrrolidine derived vinylcyclobutanol into a cyclohexanone 6 or a cyclo-hexenone 7.23 Rearrangement to five-membered rings competes with this ring enlargement and becomes the main reaction course on treatment with hydrochloric acid or boron trifluoride.23... 

The sulphur atom of alkyl(thioalkyl)phosphonium salts forms a new onium centre on triethyloxonium tetrafluoroborate alkylation in nitromethane848,849 (thiocetals see above). Phosphonium ketene acetals are potential alkylating agents for phosphorus dithioic acid anions in non-aqueous, aprotic and aqueous media and in phase-transfer catalysis conditions296 (reaction 263). It is suggested that onium ketene acetals react by nucleophilic attack on the methyl group of the acetal. 

Hydrolysis of nitriles.1 N itriles are converted to thioamides by reaction with I (2 equivalents) at 40° overnight. Under these conditions most other functional groups are stable. Kinetic studies indicate that the reaction with nitriles is a two-step process, the first of which is analogous to an enc reaction to give a. Thioamides arc particularly useful precursors to amines by the method of Borch (2, 430 431), reaction with triethyloxonium tetrafluoroborate followed by reduction withNaBHj..- ... 

In the course of O-alkylation with triethyloxonium tetrafluoroborate, the lactim ethers of 1,4-dihydro-3(2//)-isoquinoIinones were obtained (75JMC395). These are useful starting materials for reactions with amines resulting in 1,4-dihydro-3-isoquinolylamines (85EUP139296). By means of bifunctional amines, further condensed hetero-ring compounds could be synthesized (73JMC633). 

Oxadiazoles are difficult to alkylate. However, N-methylfurazinium salts are formed on heating furazans with dimethyl sulfate (74AJC1917,95JCS(P1)1083) the reaction is approximately 7 and 62 times slower, respectively, than the corresponding methylations of 1,2,5-thiadiazole and isoxazole. The N-ethyl salts of furazan itself and 3-phenylfurazan have been prepared using triethyloxonium tetrafluoroborate (64JA1863). 

The metallation of 3-methyl-4//-5,6-dihydro-l,2-oxazine has been shown to take place at the methyl group with hindered bases and at the methylene group with unhindered bases (81JA5916). Deprotonation of (753) with lithium dimethylamide at -65 °C followed by reaction with benzyl bromide gave (754) in 85% yield. This product was converted to enone (755) by reaction first with triethyloxonium tetrafluoroborate to produce an oxoiminium salt. The salt was stirred with trimethylamine and the resulting a,/3-unsaturated imine hydrolyzed with wet silica gel to the enone (Scheme 174). The lithiated derivative of (753) serves as a synthon for the unknown a-anion of methyl vinyl ketone. 

Whereas the reaction of the linearly fused 117/-pyrido[2,l -h]quina-zolin-ll-one (27) with alkylating agents (dimethyl sulfate at 120°C, and tri-ethyloxonium tetrafluoroborate in methylene chloride at 20°C) gave exclusively 7V(5)-alkylated quaternary salts (107), that of the isomeric angularly fused 6//-pyrido[l,2-a]quinazolin-6-one (28) with the soft methyl iodide afforded only the iV(5)-methyl quaternary iodide (108, X = I). The reactions of 28 with the hard dimethyl sulfate and triethyloxonium tetrafluoroborate yielded a mixture of 5-methyl-6-oxo-6//-pyrido[l,2-a]quinazolinium salts (108) and 6-alkoxypyrido[l,2-a]quinazolinium salts (109) (90JHC2005). 

Drijvers and Goethals 52) have reported that excess sulphide functions (monomer and polymer) and diethyl ether have no detectable effect on the dissociation of two sulphonium tetrafluoroborate salts in methylene chloride and nitrobenzene, when present in similar proportions to those in corresponding polymerisation reactions. In contrast to this, however, Jones and Plesch 51) have shown that the dissociation constant of triethyloxonium hexafluorophos-phate in methylene chloride at 0°C increases by a factor of - 2 when small quantities of tetrahydrofuran are added. The latter molecule has a lower dielectric constant than methylene chloride and might therefore be expected to reduce dissociation. These workers have interpreted their results in terms of specific solvation of the cation by ether molecules, with subsequent reduction in the effective charge density of the positive ion and hence in the coulombic force favouring ion pairing, e.g. 

Vinyliodonium tetrafluoroborates.l These salts are obtained with retention of configuration by reaction of vinylsilanes with iodosylbenzene activated with triethyloxonium tetrafluoroborate (equation I). 

Lactim ether formation from 2,3,4,5-tetrahydro-l//-l-benzazepin-2-one on reaction with dimethyl sulfate and triethyloxonium tetrafluoroborate has been described, and reactions of the lactim ether with a number of primary amines were reported <2003CHE344>. 

Arylmethyl(homobenzyl)ethylsulfonium salts are appropriate substrates for Suzuki-type coupling reactions. In this reaction, performed on a polymer-bound sulfonium tetrafluoroborate, the benzyl fragment on the sulfur atom was transferred to the boronic acid residue. The sulfonium salt was prepared from an al-kylthiol resin by alkylation with a substituted benzyl halide to give thioether 98 and subsequent alkylation with triethyloxonium tetrafluoroborate. Reaction with a boronic acid derivative yielded diaryl methanes 99 [94] (Scheme 6.1.22). 

The best procedure for the preparation of these compounds involves alkenylsilanes and iodosylbenzene activated by either triethyloxonium tetrafluoroborate or boron trifluoride etherate. The reaction proceeds stereospecifically with retention of configuration. 

Figure 1 shows the results obtained when samples of triethyloxonium tetrafluoroborate are allowed to react to completion with a series of polyglycols in 1,2-dichloroethane solution. Equal weights (0.86 g) of polymer were taken for all experiments so the essential difference between runs with polymers of molecular weight 1540,4000, 6000 and 20.000 lies in the hydroxyl content of the solutions. With sufficient oxonium salt the polymers were completely degraded and the only reaction product was dioxane. 

Table 1. Reaction products obtained from propylene oxide (166 g) and triethyloxonium tetrafluoroborate (40 mmoles) (7)...

Kern (7) and Entelis and co-workers (15-17) found tetramer and small amounts of larger rings when the monomer was treated with borontrifluoride or triethyloxonium tetrafluoroborate. With the first initiator the ratio of tetramer to polymer is greater in the early stages of the reaction than after longer reaction periods (15). From this observation it was concluded that tetramer and polymer are formed by two independent reaction paths. The ratio of oligomers to polymer increased with temperature (16)-... 

The cationic polymerization of styrene sulfide has been reinvestigated by Van Craeynest (15). With triethyloxonium tetrafluoroborate as initiator, a rapid and quantitative polymerization was observed, followed by a slow degradation of die polymer to a mixture of cis and tram 2,5-diphenyl-l, 4-dithiane and as and tram 2,6-diphenyl-1,4-dithiane. Since the BF4 counter ion is not capable of forming a covalent bond, a back-biting reaction via sulfonium ions seems the plausible mechanism for the dimer formation. The polymerization initiated with dimethyl sulfate showed the same characteristics a fast polymerization is followed by degradation to the same mixture of isomeric diphenyl- 1,4-dithianes. However, the mwts-2,5-diphenyl derivative was the only isomer that crystallized from the solution. It is therefore reasonable to accept that with dimethyl sulfate also, the cyclic dimers of styrene sulfide are formed by a back-biting type of degradation of the polymer and not by the mechanism shown above. 

The use of an unsaturated nucleophile to introduce into the chain end of the macromolecule a double bond has also proved successful for the synthesis of poly-THF macromonomers. The oxolane polymerization is started with any efficient initiator. When the growing chains have reached the desired length, the unsaturated deactivator is added. The reaction between the oxonium sites and the nucleophile should be fast and free of side reactions. Various unsaturated nucleophiles have been employed, e.g. p-vinylphenoxide used by Asami50). The THF polymerization was initiated with triethyloxonium tetrafluoroborate and carried out atO °C. Addition of the nucleophile (obtained by reaction of the phenol with NaH) yields the corresponding macromonomer the structure of which was characterized by various techniques ... 

Alkylation with triethyloxonium tetrafluoroborate of a 1,2,3,4-thiatriazole substituted in the 5-position with an aryl or an alkylthio group gives a thiatriazolium salt (81 equation 52) (76AHC(20)145). With an alkyl- or aryl-amino group in the 5-position, however, a 4,5-disubstituted thiatriazoline is formed (see Section 4.28.2.5.2). Under similar alkylation conditions 5-ethoxythiatriazoles decompose completely to nitrogen, sulfur and ethyl cyanate. This is the normal thermal decomposition reaction of 5-alkoxythiatriazoles (see Section 4.28.2.3.l(i)) <76AHC(20)145). 

The most convincing evidence is Vofsi and Tobolsky s (24) work with 14C-labelled triethyloxonium tetrafluoroborate at 0°C. They found good agreement among the molecular weights calculated from the amounts of catalyst charged, determined by 14C end-group analysis and determined by vapor pressure osmometry. Dreyfuss et al. have also obtained NMR data on this initiation reaction (9). The spectra are entirely consistent with Reaction 4. No side reactions are indicated. 

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