[13494-80-9]  · Te  · Tellurium  · (MW 127.60)

(N-tosylimine synthesis;5 catalyst for synthesis of alkenes,6,7 ureas,8 isothiocyanates,9 and for reduction of various functional groups3)

Physical Data: mp 449.8 °C; bp 1390 °C; d 6.25 g cm-3.

Solubility: insol any solvent unless tellurium reacts with it.

Form Supplied in: powder, pieces, or ingot.

Preparative Methods: amorphous form of tellurium can be obtained by reduction of tellurous acid (H2TeO3) with Sulfur Dioxide or Hydrazine hydrate as brown to gray powder.

Handling, Storage, and Precautions: storage under inert atmosphere is recommended since tellurium is oxidized gradually in air at room temperature. Use in a fume hood.

Synthesis of Organotellurium Compounds.1c,d,2

Elemental tellurium reacts with organolithium, -sodium, and Grignard reagents to form RTeM (M = Li, Na, MgX) at room temperature. This reaction and reduction of tellurium to its dianion (see below) provide a convenient synthetic route to a variety of organotellurium compounds by combination with appropriate subsequent reactions, as exemplified in eq 1. Tellurium also directly reacts with some organic halides to give diorganyltellurium dihalides, but the synthetic utility of this reaction is limited to the use of alkyl iodides or to the formation of cyclic tellurides from dihaloalkanes.

Selective Reduction.2,3

Among several methods which have been developed for the reduction of elemental tellurium to its dianion species, synthetically the most convenient are Sodium Borohydride in EtOH,2a Lithium Triethylborohydride in THF,2b rongalite-C (Sodium Hydroxymethanesulfinate) in H2O,2c Sodium Hydride in DMF2d or NMP.2e Salts of hydrogen telluride which can be formed (frequently referred to as M2Te or MTeH where M = Li or Na, see Hydrogen Telluride and Sodium Telluride) reduce aromatic aldehydes, C-C double bonds conjugated with carbonyl or aryl groups, imines and iminium salts, enamines, thiocarbonyls, epoxides, and a variety of nitrogen-containing functional groups.3 They also facilitate dehalogenation, desulfurization, desulfonylation, dealkylation or deacylation of carboxylates, deallylation of allylic ethers, etc. Metallic tellurium also reacts with sodium diethyl phosphite in EtOH or THF to give Sodium O,O-Diethyl Phosphorotelluroate, which acts as a reducing agent in a similar manner.4 These tellurium reagents regenerate elemental tellurium after the reaction, and some reductions have been performed successfully by the use of a catalytic amount of tellurium.

Synthesis of N-Tosylimines.5

N-Tosylimines have been prepared in excellent yields from aldehydes, Chloramine-T, and 0.5 mol equiv of tellurium (eq 2). This reaction is proposed to involve [2 + 2] cycloaddition of an aldehyde with N,N-ditosyltellurodiimide generated in situ and subsequent cycloreversion.

Alkene Synthesis by Tellurium-Catalyzed Homocoupling.

Wittig reagents6 and benzenesulfonylbenzyllithiums7 undergo homocoupling to yield alkenes in the presence of a catalytic amount of tellurium (eqs 3 and 4). The intermediacy of tellurocarbonyl compounds in the former case was evidenced by the successful trapping with dienes to give telluracyclohexenes.

Urea Synthesis by Tellurium-Catalyzed Carbonylation of Amines.8

Primary amines are carbonylated with Carbon Monoxide using tellurium as catalyst to give an equimolar amount of the urea and hydrogen along with formamides (eq 5). Addition of nitrobenzene in the reaction media affords aniline and suppresses the generation of hydrogen and formamides.

Tellurium-Catalyzed Isothiocyanate Synthesis.9

Tellurium, like Selenium, catalyzes the synthesis of isothiocyanates from isocyanides and Sulfur in the presence of a tertiary amine such as Triethylamine, but much more efficiently (eq 6). This reaction is proposed to proceed via isotellurocyanate intermediates.

1. (a) The Physics of Selenium and Tellurium; Gerlach, E.; Grosse, P., Eds.; Springer: Berlin, 1979. (b) Irgolic, K. J. The Organic Chemistry of Tellurium; Gordon and Breach: New York, 1974. (c) Schmidt, M.; Siebert, W.; Bagnall, K. W. The Chemistry of Sulphur, Selenium, Tellurium and Polonium; Pergamon: New York, 1973. (d) Tellurium; Cooper, W. C., Ed.; Van Nostrand Reinhold: New York, 1971.
2. (a) Barton, D. H. R.; McCombie, S. W. JCS(P1) 1975, 1574. (b) Detty, M. R.; Seidler, M. D. JOC 1982, 47, 1354. (c) Tschugaeff, L.; Chlopin, W. CB 1914, 47, 1269. (d) Suzuki, H.; Padmanabhan, S.; Inouye, M.; Ogawa, T. S 1989, 468. (e) Suzuki, H.; Nakamura, T. JOC 1993, 58, 241.
3. (a) Petragnani, N.; Comasseto, J. V. S 1991, 793 and 897. (b) Back, T. G. In The Chemistry of Organic Selenium and Tellurium Compounds; Patai, S., Ed.; Wiley: New York, 1987; Vol. 2, p 91.
4. Clive, D. L. J.; Beaulieu, P. L. JOC 1982, 47, 1124.
5. Trost, B. M.; Marrs, C. JOC 1991, 56, 6468.
6. Erker, G.; Hock, R. AG(E) 1989, 28, 179.
7. Engman, L. JOC 1984, 49, 3559.
8. Kambe, N.; Kondo, K.; Ishii, H,; Sonoda, N. BCJ 1981, 54, 1460.
9. Fujiwara, S.; Shin-Ike, T.; Okada, K.; Aoki, M.; Kambe, N.; Sonoda, N. TL 1992, 33, 7021.

Noboru Sonoda & Nobuaki Kambe

Osaka University, Japan

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