Trimethyloxonium

The principal electrophiles to attack ring sulfur are either oxidants or alkylating reagents. Thiophene sulfoxide and sulfone formation is discussed in Section 3.02.2.6. Alkylating agents capable of forming thiophenium salts include trimethyloxonium tetrafluoroborate (MeaO BF ) and alkyl fluorosulfonates (ROSO2F). The salts e.g. 87) are conveniently isolated as hexafluorophosphates (88). 

Apply the same analysis to trimethyloxonium ion, MesO" a cationic electrophile. Examine the LUMO. What are the best sites for nucleophile-LUMO overlap How would electron transfer affect CO bond lengths ... 

Cleavage of the chiral auxiliary is effected in a three-step procedure commencing with quatemization of the nitrogen with methyl fluorosulfonate, methyl trlfluoromethanesulfonate, or trimethyloxonium tetrafluoroborate. Reduction of the corresponding iminium salt 19 with NaBH4 and acidic hydrolysis of the resulting product affords substituted aldehyde 5 without epimerization of either stereocenter. 

Upon treatment of telluroazepinones 57 with trimethyloxonium boron tetrafluo-ride, 4-methoxy-1,5-telluroazepines 59 were prepared in 40 5% yields (98H631). These compounds are thermally unstable. 

Teiuethyl-2,4-cyceohexadie-none, 46,115 dimenzation of, 46,117 Trimethyloxonium fluoborate, 46, 120... 

Dibenz[r,e,]azcpinium salts, e.g. 3 and 6, arc also obtained by O- and 5-alkylation of 6,7-dihydro-5//-dibenz[f,e]azepin-7-ones 2 and -7-thiones 5 with trimethyloxonium tetrafluo-roborate.181 iodomethane,181 or methyl trifluoromethanesulfonate.12 Treatment of the tri-fluoromethanesulfonates 3 and 6 (X = OTf), or the tetrafluoroborate 6 (X = BF4) with 2 M sodium hydroxide in dichloromethane liberates the free bases 4 and 7, respectively.7,181... 

A solution of the benzoxazepinone 2 (4.2 g, 26 mmol) in CH2C12 (200 mL) was stirred under N2 and trimethyloxonium tetrafluoroborate (4.0 g, 27 mmol) was added. The mixture was stirred for 24 h and then neutralized with coned aq K2C03. The filtered solution was evaporated and the residue distilled in a Kugelrohr apparatus to give the product yield 4.2 g (90%) pale-yellow oil. 

The thiazepinone 6 reacts with trimethyloxonium tetrafluoroborate in diuhloromethane, followed by aqueous sodium hydrogen carbonate, to give 2,7-di- c-y7-butyl-5-methoxy-l,4-thiazepine (7) in 65 % yield. No further details were reported.48... 

The benzothiazepinone 2 is converted into the Ar-methyl derivative 5 by treating its sodium salt with iodomethane and into 5-methoxy-l,4-benzothiazepine (6) with trimethyloxonium tet-rafluoroborate. Compound 6 gives the S-methyl salt 7 on methylation with iodomethanc/sil-ver(I) tetrafluoroborate.49... 

A stirred solution of the benzothiazepinone 2 (6.0 g, 33.9 mmol) in CH2C12 (200 mL) was treated with trimethyloxonium tetrafluoroborate (5.4 g, 36.5 mmol) and the mixture was stirred for 22 h. An excess of coned aq K2C03 was added, the mixture was filtered and the organic layer was separated and dried. Evaporation, followed by chromatography (silica gel, CH2C12) gave 6 as a yellow oil yield 5.8 g (89%). 

B. Methyl 4-Acetoxyhenzoate. A 100-ml., one-necked, round-bottomed flask is charged with 1.63 g. (0.011 mole) of trimethyloxonium... 

Trimethyloxonium fluoborate is only slightly soluble in dichloromethane. However, the use of a two-phase mixture presents no difficulties in either experimental procedure or yield. 

Dimethylquinoxaline and trimethyloxonium tetrafluoroborate gave 1,4,6,7-tetramethylquinoxalinediium bis(tetrafluoroborate) (214) (excess synthon. 

The previously-reported alkylation reactions of aminocyclophosphazenes by trimethyloxonium fluoroborate, Me30BF4, have been extended. - With the dimethylamino-derivatives, N3P3Cl8-n(NMe2) (n = 1—4, or 6), a series of monomethylated derivatives, e.g. (44), was obtained, in which... 

The diquaternary salt 21 of 1,2,4-thiadiazole 1 is obtained when trimethyloxonium tetrafluoroborate is used as the methylating agent (Equation 4) <1972JOC2259>. 

Optically active sulfonium and selenonium salts are well known and the stereochemistry of the isomers has been studied.1 3 Optically active cyclic diaryl(alkoxy)-sulfonium salts 14, 15, and 16, stabilized by intramolecular sulfur-oxygen interaction, were synthesized in 2000 by reacting optically active spirosulfuranes with trimethyloxonium tetrafluoroborate.29 The absolute configurations were assigned on the basis of the reaction mechanism. The sulfonium salts were hydrolyzed in KHC03aq. to yield optically active sulfoxides in over 86% ee (Scheme 7). 

Dimethyl ether, with boron trifluoride diethyl ether-ate and epichlorohydrin to give trimethyloxonium te-trafluoroborate, 51, 142... 

TRIMETHYLOXONIUM TETRAFLUORO-BORATE, 51, 142 Trimethyloxonium tetrafluoro-borate, reactions of, 51,... 

Perhaps the most effective synthesis, albeit an expensive one, involves the direct methylation of alkylimidazoles using trimethyloxonium tetrafluoroborate with concomitant formation of the tetrafluoroborate anion as shown in Scheme 4.3 [12]. This is a single step reaction in which no chloride is present at any stage of the synthesis. The only by-product from this reaction is dimethyl ether which is a volatile and inert gas and it is easily removed. 

The vinylketene complex 140.g was shown to react toward electrophiles at the ketene oxygen. Although iodomethane had no effect, reaction with trimethyloxonium tetrafluoroborate caused methylation to produce the cationic complex 143 in fair yield. 

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