(Methoxycarbonylsulfamoyl)triethylammonium Hydroxide1

[29684-56-8]  · C8H18N2O4S  · (Methoxycarbonylsulfamoyl)triethylammonium Hydroxide  · (MW 238.35)

(dehydration agent1)

Alternate Name: Burgess reagent.

Physical Data: mp 76-79 °C.

Solubility: sol benzene, toluene, THF, triglyme, acetonitrile.

Form Supplied in: colorless solid.

Preparative Method: although the Burgess reagent is commercially available, it can be easily synthesized in two steps:1a the reaction of anhydrous methanol with Chlorosulfonyl Isocyanate followed by the addition of Triethylamine affords the reagent in good yield.

Handling, Storage, and Precautions: moisture sensitive; the use of anhydrous solvent and atmosphere in reactions with this reagent is recommended.

Formation of Carbamates.

The reaction of primary alcohols with the Burgess reagent (1) produces alkyl N-methoxycarbonylsulfamate salts, which decompose on thermolysis via an SN2 (or SNi) mechanism to give methyl urethanes (eqs 1 and 2).1a,b The products are isolated in good yields. Hydrolysis of the carbamate produces primary amines. Transformations of alcohols to amines are often multistep syntheses; therefore this reaction provides a distinct advantage over the existing methodology for such substitution reactions.

It was noted that when this reaction was applied to allylic alcohols, either elimination (see below) or an SNiŽ rearrangement ensued.1c The fate of this reaction can be determined by the experimental conditions employed. Whereas the reaction in triglyme gave good yields of dienes (eq 3), thermal decomposition of the N-methoxycarbonylsulfamate intermediate at 80 °C as a solid provided >90% of the allylurethane product (eq 4).

Formation of Alkenes.

The products of the reaction of the Burgess reagent with secondary and tertiary alcohols decompose smoothly at temperatures between 30 and 80 °C in a variety of solvents to give alkenes.1 The stereochemical course of the reaction was established to be stereospecific cis elimination. This reaction minimizes the type of rearrangement products that are typical for carbonium ion-mediated elimination reactions. For example, the reaction of the Burgess reagent with 3,3-methyl-2-butanol gave three products in the ratios given in eq 5.1a The last two alkenes were generated as a consequence of the Wagner-Meerwein rearrangement, whereas the first product formed by direct b-proton removal. The choice of solvent did not affect the product ratios significantly. Usually, competition between the Wagner-Meerwein rearrangement and b-proton abstraction lies entirely in the direction of the former, which is not seen when the Burgess reagent is used.

The reaction of the Burgess reagent with 2-endo-methylbicyclo[2.2.1]heptan-2-ol afforded a mixture of the two cycloalkenes shown in eq 6.1a The ratio of the products was unexpectedly 1:1, an observation which was attributed to the steric effects of the endo C-5 hydrogen, whereby the rate of proton abstraction at C-3 would be attenuated. No rearrangement products were reported. The reaction in eq 7 proceeded to give the sole product shown; no evidence for the formation of 2-cyclopropylidenepropane was found on grounds that the b-cyclopropyl hydrogen is sterically encumbered and unavailable for elimination.1a The reaction in eq 8 afforded a product mixture favoring the (Z)-isomer.2 The selectivity is somewhat less in the case of acid-catalyzed dehydration of the same compound. It is noteworthy that similar CS2-mediated dehydrations in the presence of base require pyrolysis at temperatures exceeding 200 °C.2 Some related applications for the Burgess reagent are shown in eqs 9 and 10.3,4 Dehydration of eq 9 with Acetic Anhydride in the presence of Pyridine at 70 °C gave only 56% of the desired product.

The requirement for a cis elimination chemistry was discussed earlier; however, there are a few exceptional reaction outcomes reported in steroid chemistry.5 The results depicted in eqs 11 and 12 were unanticipated since the 11a-hydroxyl and 9b-hydrogen (eq 11) are trans-diaxial, as are the 3a-hydroxyl and 4b-hydrogen in eq 12. These results are rationalized by an intramolecular 1,2-hydrogen transfer. For example, it was suggested for eq 11 that a C-11 cation is formed first, which subsequently undergoes an intramolecular hydrogen transfer from C-9 to C-11. The resultant C-9 carbocation was postulated to be quenched by the loss of a hydrogen from C-11 and the formation of the D9-double bond.5

Formation of Dienones and Furanones.

Furanones are formed typically by treatment of a-hydroxy enones with acid; the reaction is presumed to proceed via an acid-labile dienone, although no direct evidence for the existence of such an intermediate has been demonstrated. It has been shown that a-hydroxy enones undergo dehydration in the presence of the Burgess reagent to give isolable dienones, which are cyclized to give the corresponding furanones in a separate acid-catalyzed step (eq 13).6

Formation of Vinyltributyltin Compounds and Tributyltin Isocyanate.

The use of the Burgess reagent in the facile formation of vinyltributyltin compounds has been reported.7 This type of molecule is otherwise typically synthesized under drastic flash pyrolytic conditions. Reaction of the butyltin Grignard reagent with ketones results in tertiary alcohols, which in the presence of the Burgess reagent furnish the vinytributyltin products (eq 14).

It was discovered that a side reaction during the vinyltributyltin formation, was the production of tributyltin isocyanate.8 The formation of tributyltin isocyanate could account for the major portion of the product mixture when cyclic ketones are used, an observation which was attributed to the thermal instability of the intermediary organotin alcohols. These reagents decompose at elevated temperatures to the corresponding ketone and tributyltin hydride, which react with (1) to give rise to the isocyanate (eq 15). Correspondingly, it has been shown that tin hydride reduction of (1) gives tributyltin isocyanate in quantitative yield (eq 16).

Formation of Nitriles.

Dehydration of the primary amide function by the Burgess reagent takes place under mild conditions (eqs 17 and 18), and there is often no need for protection of many functionalities in more complex molecules; the reagent has been shown to tolerate alcohols, esters epoxides, ketones, carbamates, and secondary amides.9 Excellent chemoselectivity is observed in this reaction, which takes place at room temperature.

Electrophilic Addition.

The ethyl analog of (1), (ethoxycarbonylsulfamoyl)triethylammonium hydroxide (2), has also been reported.10 Compound (2) has been shown to undergo electrophilic addition to alkenes in average to good yields (eqs 19 and 20).

1. (a) Burgess, E. M.; Penton, H. R.; Taylor, E. A. JOC 1973, 38, 26. (b) Burgess, E. M.; Penton, H. R.; Taylor, E. A.; Williams, W. M. OSC 1988, 6, 788. (c) Burgess, E. M.; Penton, H. R.; Taylor, E. A. JACS 1970, 92, 5224.
2. McCague, R. JCS(P1) 1987, 1011.
3. Stalder, H. HCA 1986, 69, 1887.
4. Goldsmith, D. J.; Kezar, H. S. TL 1980, 21, 3543. Marino, J. P.; Ferro, M. P. JOC 1981, 46, 1912. Crabbe, P.; Leon, C. JOC 1970, 35, 2594.
5. O'Grodnick, J. S.; Ebersole, R. C.; Wittstruck, T.; Caspi, E. JOC 1974, 39, 2124.
6. Jacobson, R. M.; Lahm, G. P. JOC 1979, 44, 462.
7. Ratier, M.; Khatmi, D.; Duboudin, J. G.; Minh, D. T. SC 1989, 19, 285.
8. Ratier, M.; Khatmi, D.; Duboudin, J. G.; Minh, D. T. SC 1989, 19, 1929.
9. Claremon, D. A.; Phillips, B. T. TL 1988, 29, 2155.
10. Atkins, G. M.; Burgess, E. M. JACS 1972, 94, 6135. Atkins, G. M.; Burgess, E. M. JACS 1968, 90, 4744.

Pascale Taibi & Shahriar Mobashery

Wayne State University, Detroit, MI, USA

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