Potassium Selenocyanate1


[3425-46-5]  · CKNSe  · Potassium Selenocyanate  · (MW 144.08)

(synthesis of organoselenocyanates;1 deoxygenation of epoxides;2,3 isomerization of disubstituted alkenes;4 synthesis of selenoaldehydes and selenoketones;5,6 in combination with Me3SiCl, selective cyanosilylation of aldehydes7)

Physical Data: mp 100 °C; d 2.347 g cm-3.

Solubility: sol H2O, DMF, DME, HMPA, MeCN, MeOH; slightly sol THF.

Form Supplied in: colorless crystalline solid; widely available.

Handling, Storage, and Precautions: crystalline KSeCN is hygroscopic and decomposes with elimination of selenium upon prolonged exposure to air. It should be stored in sealed containers. KSeCN is highly toxic and foul smelling. Use in a fume hood.

Organic Selenocyanates.

Organoselenocyanates are useful synthetic intermediates that participate in a variety of reactions.1 KSeCN is a versatile reagent for the preparation of organoselenocyanates. Nucleophilic displacement of halides and tosylates with KSeCN is the most convenient route to aliphatic selenocyanates, whereas nucleophilic displacement of diazo group is preferred in aromatic compounds.1 Owing to the high nucleophilicity of selenium,8 the selenocyanate ion reacts predominantly at selenium in reactions at electrophilic carbon centers. This reactivity contrasts that of their sulfur analog, the thiocyanate ion, which reacts at both sulfur and nitrogen.9 Electrophilic substitution reactions involving dicyanodiselenide, (SeCN)2, obtained by oxidation of KSeCN, also have been used for the preparation of organoselenocyanates.1,10,11 Other known selenocyanate salts include AgSeCN, CsSeCN, (Me4N)SeCN, and LiSeCN.Et2O.12,13 The latter offers greater solubility compared to KSeCN and could represent a useful alternative source of selenocyanate ion in less polar solvents.12 Synthetic organic application of KSeCN originate mainly from the synthesis and reactivity of organoselenocyanates. Some potentially promising synthetic organic transformations based on the chemistry of organoselenocyanates derived from KSeCN are summarized below.

Deoxygenation of Epoxides.

Epoxides can be deoxygenated upon treatment with KSeCN in polar protic solvents at 23-65 °C to afford alkenes with retention of configuration (eq 1).2,3 The reaction depends on the solvent; best results are obtained in polar protic solvents such as H2O/MeOH, while the reaction fails in aprotic solvents such as DMF and DMSO.3 The reaction proceeds in high yields for straight chain terminal epoxides, but for cyclic epoxides the reactivity is varied.3 For instance, reaction of cyclohexene oxide affords cyclohexene in a quantitative yield at 23 °C; however, epoxides of cyclopentene and cyclooctene remain unreacted even after prologed heating at 65 °C.3 KSeCN-mediated deoxygenation of epoxides has been utilized in the synthesis of (+)-aucantene and other selectively functionalized cyclohexenes.14

Isomerization of Disubstituted Alkenes.

Conversion of disubstituted alkenes to bromohydrins followed by sequential treatment with KSeCN in DMF and a base results in overall isomerization of the starting alkenes (eq 2).4 The reaction of bromohydrin with KSeCN results in nucleophilic displacement of bromide with inversion of configuration to stereospecifically afford the a-hydroxy selenocyanate intermediate, treatment of which with a base affords the isomerized alkenes.

Synthesis of Selenoaldehydes and Selenoketones.

Certain organoselenocyanates derived from KSeCN undergo fluoride-5 and base-induced5,6 elimination of cyanide to afford highly reactive selenocarbonyl intermediates (eqs 3 and 4). These selenocarbonyl intermediates exhibit rich cycloaddition chemistry (Diels-Alder and 1,3-cycloadditions) to afford selenium-containing heterocycles.5,6

Selective Cyanosilylation of Aldehydes.

Trimethylsilylisoselenocyanate (Me3SiNCSe), generated in situ from the reaction of KSeCN with Chlorotrimethylsilane, can be used for the chemoselective cyanosilylation of aldehydes in presence of a catalyst (eq 5).7 Higher reactivity and yields are obtained in hexane with Zinc Chloride catalysis. Ketones do not undergo this reaction.

Related Reagents.

Potassium Thiocyanate; Sodium Thiocyanate; Isoselenocyanatotrimethylsilane.

1. (a) Bulka E. In The Chemistry of Cyanates and their Thio Deivatives; Patai, S., Ed.; Wiley: Chichester, 1977; Part 2, pp 887-922. (b) Paulmier, C. Selenium Reagents and Intermediates in Organic Synthesis; Pergamon: Oxford, 1986; pp 27-32.
2. Clive, D. L. J. T 1978, 34, 1049.
3. Behan, J. M.; Johnstone, R. A. W.; Wright, M. J. JCS(P1) 1975, 1216.
4. Van Ende, D.; Krief, A. TL 1975, 2709.
5. (a) Krafft, G. A.; Meinke, P. T. JACS 1986, 108, 1314. (b) Meinke, P. T.; Krafft, G. A. JACS 1988, 110, 8671. (c) Meinke, P. T.; Krafft, G. A. JACS 1988, 110, 8679.
6. Kirby, G. W.; Trethewey, A. N. JCS(P1) 1988, 1913.
7. Sukata, K. JOC 1989, 54, 2015.
8. (a) Guanti, G.; Dell'Erba, C.; Spinelli, D. G 1970, 100, 184 (CA 1970, 73, 13 939v). (b) Parker, A. J. ACS 1962, 16, 855.
9. Ref. 1a, pp 820-886.
10. Guram, A. S. SL 1993, 259.
11. Toshimitsu, A.; Kozawa, Y.; Uemura, S.; Okano, M. JCS(P1) 1978, 1273.
12. (a) Songstad, J.; Stangeland, L. J. ACS 1970, 24, 804. (b) Meinke, P. T.; Krafft, G. A.; Guram, A. S. JOC 1988, 53, 3632.
13. (a) Paoli, D.; Chabanel, M. JCR(S) 1991, 360. (b) Birckenbach, L.; Kellermann, K. CB 1925, 58, 786 (CA 1925, 19, 1996).
14. Jäkel, E.; Schneider, M. P. CC 1987, 733.

Anil S. Guram

Massachusetts Institute of Technology, Cambridge, MA, USA

Grant A. Krafft

Abbott Laboratories, Abbott Park, IL, USA

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