· 4-Bromobenzenesulfonyl Azide
· (MW 262.08)
(1,3-dipolar reagent that undergoes cycloaddition to vinyl and alkynyl ethers1)
Physical Data: mp 54.5-56 °C.
Solubility: sol most organic solvents.
Preparative Method: by the reaction of 4-Bromobenzenesulfonyl Chloride with excess Sodium Azide in a water-ethanol mixture.2,3
Purification: crystallization from ethanol.
Handling, Storage, and Precautions: should be used in solution. Azides are prone to violent detonation upon thermal, electrical, and mechanical shock.
The principal use of p-bromobenzenesulfonyl azide is in 1,3-dipolar cycloaddition reactions with functionally substituted alkenes. The reagent has been used at ambient temperature and pressure to convert simple trimethylsilyl4 and methyl5 enol ethers of cyclic ketones to ring-contracted p-bromobenzenesulfonimidates, and thence to the corresponding amides, esters, or acids (eqs 1 and 2).
At high pressure (~15 kbar) the normally more sluggish t-butyldimethylsilyl enol ethers of cyclic ketones react in good yield to afford the ring contracted product (eq 3).6,7
The chemo-, regio-, and stereoselectivity of the ring contraction process has been demonstrated with a variety of dienol ethers obtained by dissolving metal reduction of aromatic methyl ethers (eqs 4 and 5).8
Methyl enol ethers which are unreactive under ambient conditions react in good yield to afford the corresponding p-bromobenzenesulfonimidates under the influence of low-wattage ultrasound (eqs 6 and 7).9
Cycloaddition of p-bromobenzenesulfonyl azide to alkynyl ethers affords equilibrium mixtures of triazole and diazocarboximidate. In the case of the ether in which both the carbon and the oxygen substituents of the alkynyl ether are methyl, only the triazole is found (eq 8).10
- 1. 1,3-Dipolar Cycloaddition Chemistry; Lwowski, W., Ed.; Wiley: New York, 1984; Vol. 1, p 817.
- 2. Curtius, T. JPC 1930, 125, 303.
- 3. Reagan, M. T.; Nickon, A. JACS 1968, 90, 4096.
- 4. Wohl, R. A. HCA 1973, 56, 1826.
- 5. Wohl, R. A. TL 1973, 3111.
- 6. Dauben, W. G.; Hart, D. J. JOC 1977, 42, 922.
- 7. Dauben, W. G.; Bunce, R. A. JOC 1982, 47, 5042.
- 8. Goldsmith, D. J.; Soria, J. J. TL 1986, 27, 4701.
- 9. Goldsmith, D. J.; Soria, J. J. TL 1991, 32, 2457.
- 10. Himbert, G.; Regitz, M. CB 1972, 105, 2963.
Emory University, Atlanta, GA, USA
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