· Benzeneseleninyl Chloride
· (MW 207.52)
(introduction of a,b-unsaturation in ketones and esters;1 oxidation of amines2 and aldoximes;3 halogenation of alkenes4 and aromatic compounds5 with aluminum halides)
Physical Data: mp 75 °C.
Solubility: sol CH2Cl2, THF.
Preparative Method: benzeneseleninyl chloride is obtained from the oxidation of Benzeneselenenyl Chloride in CH2Cl21 or CCl46 with Ozone.
Handling, Storage, and Precautions: benzeneseleninyl chloride crystals are extremely hygroscopic and care must be taken to avoid moisture. Solutions in CH2Cl2 are stable for weeks when stored at -15 °C. Selenium compounds are potentially toxic and should be handled in a fume hood.
Ketone and ester enolates react with benzeneseleninyl chloride to give a-phenylseleninyl intermediates, which undergo selenoxide elimination to form enones upon warming to room temperature.1,7 Since the conventional two-step selenenylation/oxidation procedure gives higher yields with fewer byproducts (see Benzeneselenenyl Bromide, Benzeneselenenyl Chloride, and Diphenyl Diselenide), the use of benzeneseleninyl chloride is recommended specifically to avoid competing or preferential oxidation (eq 1).7
Primary aryl-substituted amines are oxidized cleanly to ketones and nitriles, presumably via an intermediate seleninamide.2 Although aldoximes are converted to nitriles in 71-96% yields at rt, comparable results are obtained using readily available benzenesulfenyl chloride or benzeneselenenyl chloride.3
The addition of an equivalent of Aluminum Chloride to a solution of benzeneseleninyl chloride in CH2Cl2 produces a complex which chlorinates electron-rich aromatic compounds, such as anisole, diphenyl ether, and N,N-dimethylaniline, exclusively in the para position.5 This complex also regioselectively chlorinates thiophenes8 and converts alkenes to vinyl chlorides (eq 2).4,9 Similarly, a highly efficient brominating complex is formed when aluminum bromide is combined with benzeneseleninyl chloride (eq 3).8
- 1. Reich, H. J.; Renga, J. M.; Reich, I. L. JACS 1975, 97, 5434.
- 2. Czarny, M. R. SC 1976, 6, 285.
- 3. Sosnovsky, G.; Krogh, J. A. ZN(B) 1979, 34B, 511.
- 4. Kamigata, N.; Satoh, T.; Yoshida, M. BCJ 1988, 61, 449.
- 5. Kamigata, N.; Satoh, T.; Yoshida, M.; Matsuyama, H.; Kameyama, M. BCJ 1988, 61, 2226.
- 6. Ayrey, G.; Barnard, D.; Woodbridge, D. T. JCS 1962, 2089.
- 7. Smith, A. B., III; Empfield, J. R.; Rivero, R. A.; Vaccaro, H. A. JACS 1991, 113, 4037.
- 8. Kamigata, N.; Satoh, T.; Yoshida, M.; Matsuyama, H.; Kameyama, M. PS 1990, 53, 29.
- 9. Kamigata, N.; Satoh, T.; Yoshida, M.; Kobayashi, M. CL 1987, 345.
James M. Renga
DowElanco, Indianapolis, IN, USA
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