Methyl(methylene)oxonium Hexafluoroantimonate


[41581-97-9]  · C2H5F6OSb  · Methyl(methylene)oxonium Hexafluoroantimonate  · (MW 280.82)

(methoxymethylating agent; methylating agent; cationic polymerization initiator)

Preparative Methods: can be prepared either by treating Methoxyacetyl Chloride with anhydrous hexafluoroantimonic acid (see Hydrogen Fluoride-Antimony(V) Fluoride) in SO2, or by combining Chloromethyl Methyl Ether with the acid in methylene chloride.1 In both cases, the pure MeOCH2+SbF6- was obtained by washing the crude products with dry Freon 113.

Handling, Storage, and Precautions: is corrosive and moisture sensitive. It should be stored in a Teflon or Nalgene bottle under anhydrous conditions.

General Discussion.

The methyl(methylene)oxonium ion (MeOCH2+) is one of the few stable primary carbenium ions and has been a subject of many experimental and theoretical studies.5-7 The experimental investigation of the carbenium ion has been carried out both in liquid5 and gas phases.6 The hexafluoroantimonate salt is a stable crystalline compound and is capable of electrophilic addition to carbon-carbon double bonds.8 When methyl geranylate was combined with MeOCH2+SbF6-, cyclization occurred. Both epimers of the cyclization product were obtained in almost equal molar ratio (eq 1). However, when the substrate was changed to geranylacetone, one of the epimers was produced as a predominant product (eq 2). The low stereoselectivity in the case of methyl geranylate at the epimeric site is due to the decreased electron density of the a,b-unsaturated methyl carboxylic ester double bond in the molecule.

Due to the ambident nature of methyl(methylene)oxonium ion, MeOCH2+SbF6- is also capable of methylation of nucleophiles through displacement of formaldehyde. This was shown in the reaction of MeOCH2+SbF6- with benzene (eq 3).1 Toluene was obtained in high yield in the reaction.

It was reported that MeOCH2+SbF6- can also initiate cationic polymerization.9

Methoxycarbenium salts with other counterions such as ClO4-,2 BF4-,3 and SbCl64 are also known and have been used in organic synthesis.

Related Reagents.

Chloromethyl Methyl Ether.

1. Olah, G. A.; Svoboda, J. J. S 1973, 52.
2. Jaacks, V.; Frank, H.; Grunberger, E.; Kern, W. Makromol. Chem. 1968, 115, 290.
3. (a) Roitburd, G. V.; Smit, W. A.; Semenovsky, A. V.; Shchegolev, A. A.; Kucherov, V. F.; Chizhov, O. S.; Kadentsev, V. I. TL 1972, 4935. (b) Smit, V. A.; Roitburd, G. V.; Semenovskii, A. V.; Kucherov, V. F.; Chizhov, O. S.; Kadentsev, V. I. IZV 1971, 2356.
4. Komarov, B. A.; Rozenberg, B. A.; Enikolopyan, N. S. IZV 1974, 1874.
5. (a) Olah, G. A.; Bollinger, J. M. JACS 1967, 89, 2993. (b) White, A. M.; Olah, G. A. JACS 1969, 91, 2943.
6. For example, see: (a) Okada, S.; Abe, Y.; Taniguchi, S.; Yamabe, S. JACS 1987, 109, 295. (b) Kim, J. K.; Bonicamp, J.; Caserio, M. C. JOC 1981, 46, 4236.
7. For example, see: (a) Farcasiu, D.; O'Donnell, J. J.; Wiberg, K. B.; Matturro, M. CC 1979, 1124. (b) Woods, R. J.; Andrews, C. W.; Bowen, J. P. JACS 1992, 114, 850.
8. Mustafaeva, M. T.; Kuzovkin, V. A.; Smit, V. A.; Semenovskii, A. V.; Kucherov, V. F. DOK 1973, 208, 1103.
9. Rozenberg, B. A. In Cationic Polym. Relat. Processes, Proc. Int. Symp., 6th; Goethals, E. J., Ed.; Academic: London, 1984 (CA 1984, 101, 211 777a).

George A. Olah, G. K. Surya Prakash, Qi Wang & Xing-ya Li

University of Southern California, Los Angeles, CA, USA

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.