Oxonium, triethyl-, tetrafluoroborate

Triethyloxonium fluobotate [Oxonium, triethyl-, tetrafluoroborate(l-)), 59 TVTrifluoroacetylation, 122 Trimethyloxonium fluoborate [Oxonium, trimethyl-, tetrafluoroborate(l-),... 

The electrophilic substitution of the 3-aryl compounds (265, R = Ar, R = H) exemplified by the formation of 5-bromo- (265, R = Ar, R = Br) and 5-nitro derivatives (265, R = Ar, R = NOj) has been put forward as evidence against the meso-ionic formulation 265. lliis approach is unacceptable since ground state charge distribution cannot be deduced from reaction products. The aluminum-amalgam reduction of meso-ionic l,2,3-thiadiazol-4-ones (265) yields either N-mercaptoacetyl-A-arylhydrazines or Ar-acyl-A-arylbydrazines. Triethyl-oxonium tetrafluoroborate and meso-ionic l,2,3-thiadiazol-4-ones (265) yield 1,2,3-thiadiazolium tetrafluoroborates (267). The effect of solvent on the ultraviolet spectra of meso-ionic l,2,3-thiadiazol-4-ones (265) has been reported. ... 

Conjugation to the free electron pair of the thiazine nitrogen makes these 3-substituents nucleophilic. The first example is reaction of 42 <1968CHE322> and its 2-ethoxycarbonyl derivatives <1983JME559> with triethyl-oxonium tetrafluoroborate (Scheme 42). Another is the reaction of 27 with hexamethyldisiloxane to give 112 (Equation 31) <1988JME1575>. 

Ethoxy-l-azaquinolizinium tetrafluoroborate (245), prepared by the action of triethyl-oxonium tetrafluoroborate on l-azaquinolizin-2-one (238), undergoes nucleophilic displacement by m -nitrobenzoylhydrazine (Scheme 121) to afford a l-aza-2H-quinolizine derivative (246), useful as a dye intermediate (61LA(640)98). 

Alkylation with triethyl oxonium tetrafluoroborate yields two products (in the proportion 3 1) 1.2-dihydro-l-ethoxy-2-ethyl-2-4.6-triphenyl-phosphorin oxide 92 m.p. 161-162 °C, and l.l-diethoxy-2.4.6-triphenyl-X -phosphorin 71, m.p. 106 "C. 71 is known from Stade s synthesis (p. 84), 92 was identified by H-NMR. No diastereoisomers were isolated... 

Like the propagation reaction, this probably occurs by a nucleophilic attack by the THF oxygen atom on a carbon alpha to the oxygen of the trialkyl oxonium ion salt. Commonly the triethyl-oxonium ion with a tetrafluoroborate gegenion has been used (3, 24, 32). Meerwein (3) has also used the hexachlorantimonate, tetrachloroferrate, and tetra-chloroaluminate gegenions. 

Rozenberg et al. (24) have also studied the kinetics of polymerization of THF initiated by triethyl oxonium tetrafluoroborate. They generated their catalyst in situ from epichlorohydrin and the boron trifluoride-ether cofnplex and carried out their polymerizations in bulk and in... 

Alkylation of 2,5-dimethyl- or of 2,5-diphenyl-l,6,6a IV-trithia-pentalene is more difficult and it is necessary to resort to triethyl-oxonium tetrafluoroborate.77 A cyano substituent in the 3-position favors alkylation on sulfur atom in the 1-position (Eq. 35).77... 

The positive chain end is assumed to be a carbenium ion. This mechanism is not applicable to polymerizations initiated with strong alkylating agents such as triethyl-oxonium tetrafluoroborate because with these initiators no zwitter ions can be produced. Since no difference was observed between the products resulting from BF3 or from oxonium initiators (6), it is unlikely that tetramer would be formed by two different mechanisms in these two cases and consequently the proposed mechanism is dubious. 

Finally, reaction of [Ru(CN)6]4 with alkylating agents such as dimethyl sulfate31 or triethyl-oxonium tetrafluoroborate in acetone32 gives high yields of the isocyanide cations [Ru(CNMe)6j2+ and [Ru(C=N—C(Me)2 CH2 (CO)Me)6]2 respectively. Treatment of the former with simple amines leads to various carbene complexes such as [Ru(CNMe)4(C(NHMe)2)2]2+.31... 

The third and final general protocol for the hydrolysis of 5 5-acetals exploits the very easy reaction of the sulfur atom of an S-acetal with alkylating agents such as iodomethane, trimethyl- or triethyl-oxonium tetrafluoroborate, and methyl triHuoromethanesuLfonate to form the corresponding trialkylsulfonium salts. Ley s approach to the potent insect antifeedant Azadirachtin [Scheme 2 81]135,171,172 benefited from an easy S-alkylation-hydrolysis sequence. In a synthesis of Epiantillatoxin, a more difficult liberation of an aldehyde from its dithiane derivative was accomplished without rearrangement of a p,y-alkene into conjugation [Scheme 2,82].173... 

Alkylating agents commonly used are methyl iodide, dimethyl sulfate, trimethyloxonium tetrafluoroborate, and triethyl-oxonium tetrafluoroborate. When R = = C02Me or CN, the — M... 

Treatment of 4-acyl-1,2-dihydroisoquinolines, e.g., 125, with triethyl-oxonium tetrafluoroborate (Meerwein reagent) produced vinylogs of the ethoxyiminium cations in high yield, e.g., 126. Crystallization of 126 from methanol gave pure 127. In order to perform syntheses of 3-substituted ... 

Higher conversions in thiirane polymerizations, however, proceed with chain scission transfer mechanism under the influence of BF3 (C2H5)20 [192]. This is indicated by a change in the molecular weight distribution, a bimodal character. When the reaction is complete there is a marked decrease in the average molecular weight of the polymer. When thietane polymerizes with triethyl-oxonium tetrafluoroborate initiation in methylene chloride, the reaction terminates after only limited conversion [193]. This results from reactions between the reactive chain ends (cyclic sulfonium salts) and the sulfur atoms on the polymer backbone. In propylene sulfide polymerization, however, terminations are mainly due to formations of 12-membered ring sulfonium salts from intramolecular reactions [193]. 

Reactions.—Oishi and his co-workers have reported that thiono-benzoates may be converted into thiolobenzoates by means of triethyl-oxonium tetrafluoroborate in a process that is most probably initiated by the formation of the S-alkylated thiono-ester intermediate (268). However, the latter is also a powerful alkylating agent towards thiono-esters, yielding the new cationic alkylating agent (269) by the liberation of ethyl thiolo-benzoate. In the authors opinion, (268) and (269) are the important reagents in the above-mentioned reaction, whereas triethyloxonium tetrafluoroborate is effective merely as an initiator of it. The statement was... 

Although the conversion of thioamides into amines by alkylation with triethyl-oxonium tetrafluoroborate has been previously reported (c/. Vol. 4, p. 172), a considerably more detailed study has now appeared, as part of a convenient, general, and selective method for the reduction of amides to amines (Scheme 19). 

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