· N,N-Diethyl-N-methyl-N-(methylsulfonyl)ammonium Fluorosulfate
· (MW 265.32)
(reagent for converting, under mild conditions, alcohols into methanesulfonate (mesylate) esters, and primary and secondary amines into methanesulfonamides1,2)
Alternate Name: easy mesyl.
Physical Data: mp ~115 °C (dec).2
Solubility: sol dry MeCN (solutions decompose over a few hours at rt).2
Form Supplied in: not commercially available.
Preparative Method: reaction of MeSO2NEt2 with excess neat MeOSO2F at 50 °C for 72 h.2
Analysis of Reagent Purity: 1H NMR (CD3CN) d: 1.40 (t, 6H), 3.11 (s, 3H), 3.60 (q, 4H), 3.70 (s, 3H).2
Handling, Storage, and Precautions: hygroscopic; hydrolyzed by moist air (products corrosive); stable indefinitely in a sealed ampoule at rt.
N,N-Diethyl-N-methyl-N-(methylsulfonyl)ammonium fluorosulfate2), and related compounds of the general structure MeSO2+NR1R2R3 X- (X = FSO3 or CF3SO3), are effective reagents for formation, under very mild conditions, of mesylates (from alcohols) and methanesulfonamides (from amines).2 Good to excellent yields are obtained with easy mesyl plus a weakly basic tertiary amine (usually a catalytic amount) such as pyridine or dimethylaminoacetonitrile (DMAA) at temperatures ranging from -70 °C to rt, e.g. (-)-menthol (1 mmol), DMAA (10 mL) in CH2Cl2 (15 mL) at 0 °C on mixing with easy mesyl (1.2 mmol) in MeCN (1 mL) followed by workup after 10 min gave
clean (-)-menthyl mesylate (99%).2 With relatively hindered alcohols (borneol, 5a-cholestan-3a-ol) the product may show contamination with the mesylmesylate ester (ROSO2CH2SO2Me), the formation of which is (a) minimized by the use of (i) weak bases (py or DMAA as opposed to Et3N or N-ethylmorpholine) and (ii) low concentrations of the amine, and (b) maximized by (i) strong bases and (ii) premixing of easy mesyl and the base.2,3 Related N-methylsulfonylammonium salts also yield mesylates; MeSO2+NMe3 FSO3- is more readily prepared (85% yield in 1 h at rt) but is less soluble in MeCN and sometimes gives a poorer yield of the mesylate (35% vs. 80% of cyclohexyl mesylate under one set of
conditions). In a set of comparison experiments3 with 5a-cholestan-3b-ol (0 °C, excess py, 30 s) the yields with Methanesulfonyl Chloride, Methanesulfonic Anhydride, and MeSO2+NMe3 FSO3- were, respectively, <1%, 60%, and >98%. The cyclic sulfonylammonium salt prepared by N-methylation of N-methylpropanesultam with MeOSO2F is used in the preparation of 3-(trimethylammonio)-1-propanesulfonate esters (
Easy mesyl has proved useful in the preparation of fragile mesylates (e.g. t-BuOMs2), especially for immediate further transformation (eqs 1 and 2);5,6 use of MeSO2Cl in these cases gave inferior results.
- 1. Fieser, M.; Fieser, L. F. FF 1977, 6, 190.
- 2. King, J. F.; du Manoir, J. R. JACS 1975, 97, 2566.
- 3. Du Manoir, J. R. Ph.D. Thesis, University of Western Ontario, 1978.
- 4. King, J. F.; Loosmore, S. M.; Aslam, M.; Lock, J. D.; McGarrity, M. J. JACS 1982, 104, 7108.
- 5. King, J. F.; Tsang, G. T. Y.; Abdel-Malik, M. M. A.; Payne, N. C. JACS 1985, 107, 3224.
- 6. Sih, J. C.; Graber, D. R. JOC 1978, 43, 3798.
James F. King
The University of Western Ontario, London, Ontario, Canada
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