1- methyl oxonium salts

The analogous reaction, the alkylation of methyl (trimethylsilyl)methyl ether with alkyl iodide/AgBF4, and the reaction in Eq. (4.15) have been employed to prepare tertiary [(trimethylsilyl)methyl]oxonium salts. 

Alkoxy tellurium pentafluorides are good alkylating reagents. Methoxy tellurium pentafluoride converts diethyl ether to the diethyl(methyl)oxonium salt. ... 

According to analysis by n.m.r. the use of diethyl ether at this point does not cause any detectable exchange of methyl by ethyl groups in the oxonium salt. 

Because of the difficulty encountered in acetylation of the complexed alcohol, it was of interest to see if the ester complex behaves in a normal fashion. Refluxing (HaO) [Cr(AcO-A)2] in methanol or ethanol caused methyl or ethyl acetate to be formed, while refluxing in ethyl propionate formed ethyl acetate. When the potassium salt was used in place of the oxonium salt no transesterification was observed this could be due to the necessity of acid catalysis or a difference in solubility in these essentially heterogeneous systems. The oxonium salt, (H30) [Cr(AcO-A)2], appears to have typical ester reactivity. 

Under considerably increased pressure, or when strongly cooled, hydrogen sulphide and water can combine to form a crystalline compound of which the composition is probably II2S.6II20 if the temperature and pressure are allowed to revert to the normal conditions, the crystals at once dissociate into the constituent substances.6 An additive compound of methyl ether and hydrogen sulphide, (CH3)2O.H2S, melting at —148-5° C., is also capable of existence at low temperatures 7 although the nature of this compound may be allied to that of the additive compound with water, it appears more probable that the methyl ether compound is an oxonium salt. 

On warming to -20°C, methoxymethyl 57 reacts with the remaining CH3SO3F. The rhenium methyl product 55 forms, but oxonium salt or methylidene (58) intermediates are not detected. This is understandable if the methylidene 58 (or the oxonium salt) is reduced more rapidly than it is formed (Scheme 2, step d). Depending upon reaction conditions, 39 and/or... 

Since methyl dioxolane can amount to as much as ten percent of the dioxane, a termination of this kind could account for the low yield from regenerated ions but this scheme puts a lot of weight on the presence of dioxolane, a product which could, after all, arise by direct rearrangement of oxide to acetaldehyde. Furthermore, the zero order dependence on monomer does not necessarily rule out direct reaction between oxonium ion and monomer for it will be recalled that Meerwein observed that the inner oxonium salt complexed very strongly with a molecule of ether. If reaction were to occur between an ion and a monomer molecule held in this way, the rate could be independent of the monomer concentration. 

Non-deprotonated amides are weak nucleophiles and are only alkylated by trialkyl -oxonium salts or dimethyl sulfate at oxygen or by some carbocations at nitrogen [16, 83]. Alkylation with primary or secondary alkyl halides under basic reaction conditions is usually rather difficult, because of the low nucleophilicity and high basicity of deprotonated amides. Non-cyclic amides are extremely difficult to N-alkylate, and few examples of such reactions (mainly methylations, benzylations, or allyla-tions) have been reported (Scheme 6.21). 4-Halobutyramides, on the other hand, can often be cyclized to pyrrolidinones in high yield by treatment with bases (see Scheme 1.8) [84—86]. 

Sometimes the effects of solvent may not be very great. 3-t-Butyl-6-dimethylaminopyridazine reacted with methyl iodide in acetonitrile to give a 63 37 ratio of 1- and 2-methiodides. The results in hexane, benzene, carbon tetrachloride, and acetone were similar, and only in ethers [dimethoxy-methane, 79 21 tetrahydrofuran (THF), 84 16] did the product ratios vary to any extent, perhaps because the methylating agent in ethers is an oxonium salt (73ACS383). 

Friedel8 had already shown in 1875 that methyl ether combines with hydrogen chloride to give an oxonium salt (CH3)20. HCI, and it... 

The exact geometry of oxonium salts is not known. Calculations using the CNDO-2 method indicate the following structures for protonated and methylated oxirane ... 

The problem was later clarified with the finding that methylation of styryl-6-dihydropyran-2,4-dione, an analogue of yangonolactone, by diazomethane yielded a mixture of isomeric CC-pyrone and y-pyrone compounds as shown in Figure 5.4. These compounds were separated on the basis of the difference in solubilities of their hydrochloride oxonium salts in ether. The compound which formed an ether insoluble salt... 

Methyl ethyloxonium methylide, formed via methylene addition to MeOEt, either decomposes to ethylene + DME-d3, or is protonated (deuterated) by CDgOD (or D2O) impurities to give an oxonium salt, which then undergoes rapid methyl transfers to give d, d3, and dg-DME. Significant amounts of d3> d3, and d -DME are indeed observed (Tables 5 and 6), consistent with the proposed mechanism. 

Oxonium salts have been used as initiators in the polymerization of sulfides and amines as low-molecular-weight compounds (e.g. Et3OeBFJp)15,16) and as dicatio-nically living polyTHF 17,18) in the synthesis of diblock and triblock copolymers. Among alkyl esters and halides, tosylates, iodides, bromides, fluorosulfonates, and triflates were used in the polymerization of azetidines4,9,10 and aziridines 19,20). Methyl triflate forms the first alkylation product in the polymerization of 1-t-butyl-aziridine, which precipitates out of solution 19) ... 

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