[7782-49-2]  · Se  · Selenium  · (MW 78.96)

(source of selenium compounds,5,6 catalyst of alkene isomerization,43-46 dehydrogenation reagent of cyclic hydrocarbons,48-54 carbonylation catalyst of amines, alcohols, thiols, and related compounds with carbon monoxide60)

Physical Data: mp 220.5 °C; bp 685 °C; d 4.82 g cm-3.

Solubility: insol H2O and organic solvents.

Form Supplied in: powder, pieces, or ingot.

Preparative Methods: red amorphous selenium is prepared by reduction of selenious acid in cold water with reducing reagents such as sulfur dioxide and hydrazine or by oxidation of its reduced form (hydrogen selenide or its salts) with air.

Handling, Storage, and Precautions: storage under inert atmosphere is recommended since it is oxidized gradually in air at room temperature. Elemental selenium is harmless upon ingestion. Use in a fume hood.

Formation of Organoselenium Compounds.5-42

Selenium reacts with organolithium, -sodium, and -magnesium compounds at room temperature or below to form metal selenolates (RSeM, M = Li,7-10 Na,11 MgX12,13) which afford selenides by the reaction with electrophiles (eqs 1 and 2),7-11 diselenides by oxidation,12 and selenols by acidification.13

Selenium is reduced in several ways14-31 to ammonium or metal salts of hydrogen selenide or diselenide (H2Se, H2Se2) which are also useful precursors of selenides and diselenides, respectively, as well as selenoamides.28,29 Commonly used reducing reagents are rongalite (Sodium Hydroxymethanesulfinate, NaSO2CH2OH) in aq NaOH,14 Hydrazine,15,16 Li or Na in liq. NH317-20 or THF (eq 3),21 Mg in MeOH,22 Samarium(II) Iodide in THF,23 Sodium Borohydride in EtOH or H2O (eq 4),24 Lithium Triethylborohydride in THF,25 and Carbon Monoxide in H2O.26-30 Reduction with tetraalkylammonium borohydride in toluene directly affords dialkyl selenides.31

Elemental selenium reacts with hydrazones,32-34 sulfonium35 or phosphonium36,37 ylides, and a-halo carbanions38 to give selones. Sterically hindered selones can be isolated (eq 5).32-34 Less hindered selones generated in situ readily react with ylides or dienes to afford alkenes (see below) or selenium-containing heterocycles (eqs 6 and 7).35-38

Selenium adds to a diaminoalkyne39 and isocyanides40-42 to yield a diselenoamide and isoselenocyanates, respectively (eqs 8 and 9). Selenium catalyzes the formation of isothiocyanates from isocyanides and Sulfur less efficiently than Tellurium.40 Reactions of selenium with Potassium Cyanide, phosphines, or dichloromethane afford KSeCN, R3P=Se, or CSe2, respectively.5,6

Synthesis and Isomerization of Alkenes.

Selones prepared from selenium and hydrazones are useful precursors of hindered alkenes (eq 10).32-34 Wittig reagents afford alkenes with the aid of selenium (eq 11).36,37

Selenium catalyzes isomerization of alkenes at high temperatures (ca. 200 °C) to give an equilibrium mixture of cis and trans isomers when complete (eq 12).43-46 Kinetic studies suggest the intermediacy of p-complexes of alkenes with selenium. For the isomerization of cis-stilbene, the activation energy of the selenium-catalyzed reaction is about 63 kJ mol-1 (15 kcal mol-1) lower than that of thermal isomerization44 and the relative rates using selenium, Methanesulfonic Acid, and Potassium t-Butoxide are 734:20.6:1, respectively, at 190 °C.43 In the isomerization of alkenes having an allylic hydrogen, some regioisomers are formed concomitantly, especially at high temperatures, and selenium gradually loses its catalytic activity by the formation of selenium-containing byproducts.45

Reduction by the Use of Se.

Selenols, hydrogen selenide, and their salts are very useful reagents not only for introduction of selenium moieties into organic molecules but also for reduction of a variety of functional groups (for details, see Benzeneselenol and Methaneselenol, Diphenyl Diselenide, Hydrogen Selenide, Sodium Hydrogen Selenide, Lithium Selenide or Sodium Selenide, etc). What should be emphasized here is that reduction can be performed by the use of a catalytic amount of selenium or diselenides in the presence of an appropriate reducing reagent, as shown generally by eq 13.5,47

Oxidation with Selenium.

Six-membered cyclic and polycyclic hydrocarbons undergo dehydrogenation at ca. 300 °C to give aromatic compounds in moderate yields by reaction with an excess amount of metallic or amorphous selenium, where selenium is reduced to hydrogen selenide (eq 14).48,49 The selenium-promoted aromatization may be accompanied by elimination of alkyl or heteroatom groups. Ethyl groups are cleaved in preference to hydrogen with the formation of ethaneselenol (eq 15).49 Hydroxyl groups are also prone to removal (eq 16).50 Methyl groups can be lost when attached to a quaternary carbon.51 At higher temperatures, hydrogenation of double bonds, rearrangement of carbon skeletons, and cyclization of side chains may take place during aromatization (eq 17).52 This reaction is applicable to dehydrogenation of heterocyclic compounds (eq 18).53 Similar dehydrogenation with sulfur is known, but the reaction hardly proceeds with tellurium.54

Formates are oxidized to carbonates with selenium in the presence of a sodium alkoxide (eq 19). Since NaSeH formed in this process regenerates selenium upon oxidation, the reaction can be carried out by the use of a catalytic amount of selenium in the presence of oxygen.55 Formamides can be oxidized to carbamates similarly, but less efficiently.56

Selenium-Catalyzed Carbonylation and Related Reactions.

A variety of primary amines are carbonylated with carbon monoxide to give urea derivatives by the use of a catalytic amount of selenium under mild conditions in the presence of oxygen (eq 20).57-59 The turnover number of selenium reaches up to 104 at 120 °C under 30 atm of carbon monoxide.60

In these reactions, ureas are probably formed by the aminolysis of isocyanates generated by the elimination of hydrogen selenide from ammonium carbamoselenoates (3), which are formed in situ by the reaction of selenium, an amine, and carbon monoxide. Oxidation of the hydrogen selenide formed with air regenerates selenium. Some secondary amines such as Pyrrolidine, Piperidine, and dimethylamine afford corresponding ureas in excellent yields under similar conditions.60 Several control experiments suggest that carbonylation of secondary amines proceeds via aminolysis of biscarbamoyl diselenides formed by the oxidation of ammonium carbamoselenoate intermediates (3) (eq 21).61

Unsymmetrical ureas can be obtained by the addition of a different amine to the ammonium salts (eqs 22 and 23).57,62 Under mild conditions, acyclic dialkylamines other than dimethylamine do not afford corresponding ureas due to the steric hindrance. In this case, biscarbamoyl diselenides (4) are formed, which eliminate selenium to yield ureas upon pyrolysis via biscarbamoyl selenide (5) (eq 24).63 Biscarbamoyl diselenides are good carbamoylation reagents of arenes64 and cyclic ethers65 (eqs 25 and 26). Carbamoselenoates (3) quantitatively afford carbonyl selenide by acidification66 and Se-alkyl carbamoselenoates by trapping with alkyl halides (eq 24).67

This selenium-mediated carbonylation with CO was discovered and expanded by Sonoda to include synthesis of a variety of cyclic and acyclic ureas (eq 27),68-70 carbamates (eqs 28 and 29),69-73 thiocarbamates (eqs 30 and 31),70,72-75 carbonates (eq 32),76,77 thiocarbonates (eq 33),78 and heterocyclic compounds (eqs 34-37).69,70,79-81

1. Krief, A.; Hevesi, L. Organoselenium Chemistry; Springer: Berlin, 1988; Vol. 1.
2. The Physics of Selenium and Tellurium; Gerlach, E.; Grosse, P., Eds.; Springer: Berlin, 1979.
3. Schmidt, M.; Siebert, W.; Bagnall, K. W. The Chemistry of Sulphur, Selenium, Tellurium and Polonium; Pergamon: New York, 1973.
4. Organic Selenium Compounds: Their Chemistry and Biology; Klayman, D. L.; Günther, W. H. H., Eds.; Wiley: New York, 1973.
5. Paulmier, C. Selenium Reagents and Intermediates in Organic Synthesis; Pergamon: New York, 1986; Chapters 1 and 4.
6. Günther, W. H. H. In Organic Selenium Compounds: Their Chemistry and Biology; Klayman, D. L.; Günther, W. H. H., Eds.; Wiley: New York, 1973; Chapter 3.
7. Swiss, K.; Choi, W.-B.; Mohan, J.; Barnum, C.; Saindane, M.; Zima, G.; Liotta, D. HC 1990, 1, 141.
8. Gulliver, D. J.; Hope, E. G.; Levason, W.; Murray, S. G.; Potter, D. M.; Marshall, G. L. JCS(P2) 1984, 429.
9. Tiecco, M.; Testaferri, L.; Tingoli, M.; Chianelli, D.; Montanucci, M. JOC 1983, 48, 4289.
10. Anderson, J. W.; Barker, G. K.; Drake, J. E.; Rodger, M. JCS(D) 1973, 1716.
11. Brandsma, L.; Wijers, H. E.; Jonker, C. RTC 1964, 83, 208 (CA 1964, 60, 13 133c).
12. Reich, H. J.; Cohen, M. L.; Clark, P. S. OS 1980, 59, 141.
13. Foster, D. G. OSC 1955, 3, 771.
14. Bird, M. L.; Challenger, F. JCS 1942, 570.
15. Syper, L.; Mlochowski, J. S 1984, 439.
16. Kondo, K.; Murai, S.; Sonoda, N. TL 1977, 3727.
17. Rossi, R. A.; Peñéñory, A. B. JOC 1981, 46, 4580.
18. Harvey, A. B.; Durig, J. R.; Morrissey, A. C. JCP 1969, 50, 4949.
19. Shlyk, Y. N.; Bogolyubov, G. M.; Petrov, A. A. ZOB 1968, 38, 1199 (CA 1968, 69, 59 351t).
20. Brandsma, L.; Wijers, H. RTC 1963, 82, 68 (CA 1963, 59, 3762a).
21. Syper, L.; Mlochowski, J. T 1988, 44, 6119.
22. Günther, W. H. H. JOC 1967, 32, 3929.
23. Sekiguchi, M.; Tanaka, H.; Takami, N.; Ogawa, A.; Ryu, I.; Sonoda, N. HC 1991, 2, 427.
24. Klayman, D. L.; Griffin, T. S. JACS 1973, 95, 197.
25. Gladysz, J. A.; Hornby, J. L.; Garbe, J. E. JOC 1978, 43, 1204.
26. Nishiyama, Y.; Katsuura, A.; Negoro, A.; Hamanaka, S.; Miyoshi, N.; Yamana, Y.; Ogawa, A.; Sonoda, N. JOC 1991, 56, 3776.
27. Nishiyama, Y.; Hamanaka, S.; Ogawa, A.; Murai, S.; Sonoda, N. SC 1986, 16, 1059.
28. Ogawa, A.; Miyake, J.; Karasaki, Y.; Murai, S.; Sonoda, N. JOC 1985, 50, 384.
29. Ogawa, A.; Miyake, J.; Kambe, N.; Murai, S.; Sonoda, N. BCJ 1985, 58, 1448.
30. Sonoda, N.; Kondo, K.; Nagano, K.; Kambe, N.; Morimoto, F. AG(E) 1980, 19, 308.
31. Bergman, J.; Engman, L. S 1980, 569.
32. Cullen, E. R.; Guziec, Jr., F. S.; Murphy, C. J. JOC 1982, 47, 3563.
33. Back, T. G.; Barton, D. H. R.; Britten-Kelly, M. R.; Guziec, Jr., F. S. JCS(P1) 1976, 2079.
34. Back, T. G.; Barton, D. H. R.; Britten-Kelly, M. R.; Guziec, Jr., F. S. CC 1975, 539.
35. Nakayama, J.; Sugiura, H.; Hoshino, M.; Kobayashi, H. TL 1985, 26, 2201.
36. Erker, G. E.; Hock, R.; Nolte, R. JACS 1988, 110, 624.
37. Okuma, K.; Sakata, J.; Tachibana, Y.; Honda, T.; Ohta, H. TL 1987, 28, 6649.
38. Abelman, M. M. TL 1991, 32, 7389.
39. Nakayama, J.; Mizumura, A.; Akiyama, I.; Nishio, T.; Iida, I. CL 1994, 77.
40. Fujiwara, S.-I.; Shin-Ike, T.; Sonoda, N.; Aoki, M.; Okada, K.; Miyoshi, N.; Kambe, N. TL 1991, 32, 3503.
41. Sonoda, N.; Yamamoto, G.; Tsutsumi, S. BCJ 1972, 45, 2937.
42. Bulka, E.; Ahlers, K.-D.; Tucek, E. CB 1967, 100, 1367.
43. Maccarone, E.; Mamo, A.; Perrini, G.; Torre, M. JCS(P2) 1981, 324.
44. Scarlata, G.; Torre, M. JHC 1976, 13, 1193.
45. Fitzpatrick, J. D.; Orchin, M. JACS 1957, 79, 4765.
46. Fitzpatrick, J. D.; Orchin, M. JOC 1957, 22, 1177.
47. Back, T. G. In The Chemistry of Organic Selenium and Tellurium Compounds; Patai, S. Ed.; Wiley: New York, 1987; Vol. 2, p 91.
48. Libert, H.; Schmid, L. M 1967, 98, 19 (CA 1967, 66, 85 630r).
49. Cocker, W.; Cross, B. E.; Edward, J. T.; Jenkinson, D. S.; McCormick, J. JCS 1953, 2355.
50. Barker, R. L.; Clemo, G. R. JCS 1940, 1277.
51. Clemo, G. R.; Dickenson, H. G. JCS 1935, 735.
52. Ruzicka, L.; Peyer, E. HCA 1935, 18, 676.
53. Klem, R. E.; Skinner, H. F.; Walba, H.; Isensee, R. W. JHC 1970, 7, 403.
54. Suzuki, H.; Nakamura, T. JOC 1993, 58, 241.
55. Kondo, K.; Sonoda, N.; Sakurai, H. TL 1974, 803.
56. Kondo, K.; Sonoda, N.; Sakurai, H. CC 1974, 160.
57. Sonoda, N.; Yasuhara, T.; Kondo, K.; Ikeda, T.; Tsutsumi, S. JACS 1971, 93, 6344.
58. Kondo, K.; Sonoda, N.; Tsutsumi, S. CC 1972, 307.
59. Kondo, K.; Murata, K.; Miyoshi, N.; Murai, S.; Sonoda, N. S 1979, 735.
60. Sonoda, N. PAC 1993, 65, 699.
61. Fujiwara, S.-I.; Miyoshi, N.; Ogawa, A.; Kambe, N.; Sonoda, N. JPOC 1989, 2, 359.
62. Kondo, K.; Sonoda, N.; Sakurai, H. CL 1974, 1429.
63. Kondo, K.; Sonoda, N.; Yoshida, K.; Koishi, M.; Tsutsumi, S. CL 1972, 401.
64. Fujiwara, S.-I.; Ogawa, A.; Kambe, N.; Ryu, I.; Sonoda, N. TL 1988, 29, 6121.
65. Fujiwara, S.-I.; Ogawa, A.; Kambe, N.; Ryu, I.; Sonoda, N. CL 1988, 1805.
66. Kondo, K.; Yokoyama, S.; Miyoshi, N.; Murai, S.; Sonoda, N. AG(E) 1979, 18, 691.
67. Kondo, K.; Takarada, M.; Murai, S.; Sonoda, N. S 1979. 597.
68. Yoshida, T.; Kambe, N.; Murai, S.; Sonoda, N. TL 1986, 27, 3037.
69. Yoshida, T.; Kambe, N.; Murai, S.; Sonoda, N. BCJ 1987, 60, 1793.
70. Yoshida, T.; Kambe, N.; Ogawa, A.; Sonoda, N. PS 1988, 38, 137.
71. Kondo, K.; Sonoda, N.; Tsutsumi, S. CL 1972, 373.
72. Sonoda, N.; Yamamoto, G.; Natsukawa, K.; Kondo, K.; Murai, S. TL 1975, 1969.
73. Koch, P.; Perrotti, E. TL 1974, 2899.
74. Koch, P. TL 1975, 2087.
75. Sonoda, N.; Mizuno, T.; Murakami, S.; Kondo, K.; Ogawa, A.; Ryu, I.; Kambe, N.; AG(E) 1989, 28, 452.
76. Kondo, K.; Sonoda, N.; Tsutsumi, S. TL 1971, 4885.
77. Kondo, K.; Sonoda, N.; Sakurai, H. BCJ 1975, 48, 108.
78. Mizuno, T.; Nishiguchi, I.; Hirashima, T.; Ogawa, A.; Kambe, N.; Sonoda, N. TL 1990, 31, 4773.
79. Ogawa, A.; Kondo, K.; Murai, S.; Sonoda, N. CC 1982, 1283.
80. Ogawa, A.; Kambe, N.; Murai, S.; Sonoda, N. T 1985, 41, 4813.
81. Yoshida, T.; Kambe, N.; Murai, S.; Sonoda, N. JOC 1987, 52, 1611.

Nobuaki Kambe

Osaka University, Japan

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