Phenyl Selenocyanate1


[2179-79-5]  · C7H5NSe  · Phenyl Selenocyanate  · (MW 182.09)

(a specific source of nucleophilic2-5 and electrophilic selenium species6-8)

Physical Data: light yellow oil; bp 125 °C/16 mmHg, 118 °C/11 mmHg,9 104 °C/4 mmHg.10

Solubility: sol organic solvents such as THF, dichloromethane, and acetonitrile.

Analysis of Reagent Purity: spectral data (IR, NMR)10 and physical constants (bp, TLC).

Preparative Methods: diazotization of aniline followed by treatment with Potassium Selenocyanate in buffer solution containing sodium acetate;9,11 condensation reaction of Benzeneselenenyl Chloride with Cyanotrimethylsilane in dry THF or in dry dichloromethane, giving phenyl selenocyanate in almost quantitative yield.10

Purification: the product obtained by above methods contains a slight amount of Diphenyl Diselenide as impurity, which is usually not troublesome in its application to organic reactions. Pure phenyl selenocyanate can be obtained by fractional distillation or silica gel column chromatography.

Handling, Storage, and Precautions: highly toxic and unpleasant smell. Use in a fume hood.

Nucleophilic Reactions.

Phenyl selenocyanate quantitatively generates a nucleophilic selenium species (PhSe- equivalent) upon treatment with Sodium Borohydride,11 which reacts with primary alkyl bromides11 and mesylates12 to form alkyl phenyl selenides (see also Diphenyl Diselenide and o-Nitrophenyl Selenocyanate). A more useful aspect of phenyl selenocyanate is its reactions with electrophilic substrates in the presence of Tri-n-butylphosphine. For example, primary2 and secondary2,3 alcohols can be directly converted into the corresponding alkyl phenyl selenides by the reaction with phenyl selenocyanate (eq 1). Yields are somewhat lower for secondary alcohols. Aldehydes react with phenyl selenocyanate to produce cyanoselenenylation adducts in good yields (eq 2), while ketones give rearranged products in only modest yields.4 Carboxylic acids react with phenyl selenocyanate to form selenol esters in high yields (eq 3).5

Electrophilic Reactions.

Highly reactive alkenes, such as ketene acetals13 and enamines,14 react with phenyl selenocyanate in ethanol to form cyanoselenenylation products regioselectively, which can be converted into b,g-unsaturated nitriles and a,b-unsaturated aminonitriles,1 respectively (eqs 4 and 5). Simple alkenes react with phenyl selenocyanate in the presence of Lewis acids. For example, in the presence of Copper(II) Chloride or Copper(II) Bromide or in the presence of Nickel(II) Chloride or Nickel(II) Bromide, phenyl selenocyanate reacts with alkenes in methanol or phenol to produce electrophilic selenium adducts in high yields (eq 6).6 With dienes in acetonitrile, 1:2 adducts having a cyclic ether skeleton are produced (eq 7).7 In the presence of Tin(IV) Chloride, phenyl selenocyanate reacts with simple alkenes to form cyanoselenenylation products (eq 8).8

Related Reagents.

Benzeneselenenyl Chloride; Diphenyl Diselenide; o-Nitrophenyl Selenocyanate; Phenylselenium Trichloride; Phenyl Selenocyanate-Copper(II) Chloride.

1. (a) Clive, D. L. J. T 1978, 34, 1049. (b) Reich, H. J. ACR 1979, 12, 22. (c) Nicolaou, K. C.; Petasis, N. A. Selenium in Natural Products Synthesis; CIS: Philadelphia, 1984. (d) The Chemistry of Organic Selenium and Tellurium Compounds; Patai, S; Rappoport, Z., Eds.; Wiley: New York, 1986; Vol. 1. (e) Paulmier, C. Selenium Reagents and Intermediates in Organic Synthesis; Pergamon: Oxford, 1986. (f) Organoselenium Chemistry; Liotta, D; Ed.; Wiley: New York, 1987. (g) Tomoda, S.; Usuki, Y.; Fujita, K.; Iwaoka, M. Rev. Heteroatom Chem., 1991, 4, 249.
2. Grieco, P. A.; Gilman, S.; Nishizawa, M. JOC 1976, 41, 1485.
3. Sevrin, M.; Krief, A. CC 1980, 656.
4. Grieco, P. A.; Yokoyama, Y. JACS 1977, 99, 5210.
5. Grieco, P. A.; Yokoyama, Y.; Williams, E. JOC 1978, 43, 1283.
6. Toshimitsu, A.; Uemura, S.; Okano, M. CC 1977, 166.
7. Uemura, S.; Toshimitsu, A.; Aoai, T.; Okano, M. CL 1979, 1359.
8. Tomoda, S.; Takeuchi, Y.; Nomura, Y. CC 1982, 871.
9. Behaghel, O.; Seibert, H. CB 1932, 65, 812.
10. Tomoda, S.; Takeuchi, Y.; Nomura, Y. CL 1981, 1069.
11. Sharpless, K. B.; Young, M. W. JOC 1975, 40, 947.
12. Nakatsuka, S.; Yamada, K.; Yoshida, K.; Asano, O.; Murakami, Y.; Goto, T. TL 1983, 24, 5627.
13. Tomoda, S.; Takeuchi, Y.; Nomura, Y. CL 1982, 1733.
14. Tomoda, S.; Takeuchi, Y.; Nomura, Y. TL 1982, 23, 1361.

Michio Iwaoka & Shuji Tomoda

The University of Tokyo, Japan

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