Dianisyl Telluroxide1

[57857-70-2]  · C14H14O3Te  · Dianisyl Telluroxide  · (MW 357.88)

(mild oxidant for diphenols, thiols, and thio compounds;2 aldol catalyst11)

Alternate Name: bis(4-methoxyphenyl) telluroxide.

Physical Data: mp 190-191 °C.2

Solubility: poorly sol most organic solvents; sol acetic acid.

Preparative Method: by base-catalyzed hydrolysis (2N NaOH, 95 °C, 1 h) of dianisyltellurium dichloride,2 which is itself prepared by reaction of anisole with tellurium tetrachloride.3

Handling, Storage, and Precautions: stable white powder; dried in vacuo over P2O5. All manipulations must be carried out in a well ventilated hood.

Oxidation Reactions.

Ortho and para diphenols are easily oxidized by dianisyl telluroxide to quinones, and 1,2-glycols are cleaved with this reagent, whereas simple phenols and alcohols are not affected.2 Aryloxyl radicals have been observed during the reaction of 2,6-di-t-butylphenol derivatives with the telluroxide and these radicals were further oxidized, when possible, to the diphenoquinone.4 Thiols are rapidly oxidized to disulfides in high yields, even in the presence of sensitive functional groups such as aromatic amines or amino acids. A number of thio or seleno compounds have been transformed into their oxo derivatives with this reagent (eqs 1 and 2), including thionoesters, selenoesters, dithioesters, thionocarbonates, trithionocarbonates, thioketones, and xanthates. In the case of thiocamphor, a more complex sequence led to a poor yield of the ketone (10%) and to the formation of the disulfide, which was slowly converted to the dimeric thioketone. The behavior of thiourea and thioamides is dependent on the nature of the substrate and the reaction conditions. Thus thiourea and N,N-diphenylthiourea gave the corresponding ureas but N-phenylthiourea gave the dimeric 1,2,4-thiadiazole in 97% yield (eqs 3 and 4).5,6

Pyrrolidinethione gave the corresponding pyrrolidinone, but primary thiobenzamides gave either benzonitrile or underwent oxidative dimerization to 1,2,4-thiadiazoles. Thiobenzoylurea and thiobenzoylguanidine afforded only the 1,2,4-thiadiazole derivatives. Phosphines are easily oxidized to the corresponding phosphine oxides, although this method does not offer any specific advantage over classical methods.

Acylhydrazines are converted to acylhydrazides, in a reaction similar to the oxidation with diphenyl selenoxide. Arylhydrazines furnish a mixture of the corresponding arenes, of anisole, and diaryl tellurides. Benzophenone hydrazone was oxidized to diphenyldiazomethane, which was trapped with p-anisic acid. Phenylhydroxylamine afforded nitrosobenzene in 90% yield in 5 min without overoxidation.

A large number of functional groups are inert toward this telluroxide, including aldehydes, ketones, hydroxybenzoic acid esters, enamines, pyrrole, indole, amino acids, aromatic amines, isocyanides, hindered thionocarbonates, oximes, arylhydrazones, dithiolanes, sulfides, and selenides.

A polystyrene-bound diaryl telluroxide was reported to present the same spectrum of oxidizing properties as the monomeric reagent.7 The reduced reagent can be easily recovered and then reused after reoxidation. However, in the case of primary thiobenzamide, the thiadiazole was formed with the polymeric reagent in acetic acid, as well as with the monomeric dianisyl telluroxide ditosylate, whereas benzonitrile was obtained with dianisyl telluroxide.

A related reagent, bis(4-methoxyphenyl) tellurone [82342-66-3], is prepared by oxidation of the telluroxide with Sodium Periodate. It is also a mild oxidant of thiophenols to disulfides and of hydroquinones to quinones, but slightly more powerful than the telluroxide as it oxidized benzylic alcohols to benzaldehydes and benzoin to benzil. Glycols were also oxidatively cleaved.8

Catalytic Version of the Reagent.

The oxidation of thiocarbonyl compounds to their oxo analogs can also be performed with dianisyl telluride in a catalytic system with 1,2-dibromotetrachloroethane acting as a brominating agent. In the presence of aqueous base, the dibromo telluride is hydrolyzed to the telluroxide which reacts in a two-phase system.2,9 In the course of the synthesis of 1a,25-dihydroxyvitamin D3, oxidation of a cyclic hydrazine derivative was performed under these conditions to afford directly the very sensitive trans-trienic system of the vitamin (eq 5).10

Electrochemically generated telluroxide also reacts with thiobenzamide. The outcome of the reaction is directly related to the nature of the supporting electrolyte: with Bu4NOAc, benzonitrile is the only product, whereas with Et4NOTs the thiadiazole was the major or only product.7

Aldol Condensation Catalyst.

Dianisyl telluroxide acts efficiently as a mild catalyst for aldol condensations under aprotic conditions (toluene, reflux for 2 h, 0.1 equiv of the catalyst). Dibenzotropone, which cannot be obtained by using classical basic catalysis, was prepared in 96% yield with this catalyst (eq 6).11,12

However, aldol condensations with very acidic methylene compounds gave only moderate yields. This reagent also catalyzed the condensation of cinnamaldehydes with ketones and activated nitriles in high yield.13

1. Petragnani, N.; Comasseto, J. V. S 1986, 1.
2. Ley, S. V.; Meerholz, C. A.; Barton, D. H. R. T 1981, 37, Suppl. 1, 213.
3. Bergman, J.; Carlsson, R.; Sjöberg, B. OS 1977, 57, 18.
4. Barton, D. H. R.; Finet, J. P.; Giannotti, C.; Thomas, M. TL 1988, 29, 2671.
5. Newton, C. G.; Ollis, W. D.; Wright, D. E. JCS(P1) 1984, 75.
6. Hu, N. X.; Aso, Y.; Otsubo, T.; Ogura, F. BCJ 1986, 59, 879.
7. Matsuki, T.; Hu, N. X.; Aso, Y.; Otsubo, T.; Ogura, F. BCJ 1988, 61, 2117.
8. Engman, L.; Cava, M. P. CC 1982, 164.
9. Ley, S. V.; Meerholz, C. A.; Barton, D. H. R. TL 1980, 1785.
10. Andrews, D. R.; Barton, D. H. R.; Hesse, R. H.; Pechet, M. M. JOC 1986, 51, 4819.
11. Engman, L.; Cava, M. P. TL 1981, 22, 5251.
12. Akiba, M.; Lakshmikantham, M. V.; Jen, K.-Y.; Cava, M. P. JOC 1984, 49, 4819.
13. (a) Zhong, Q.; Lu, R. Yingyong Huaxue 1990, 7, 89 (CA 1991, 114, 61 639). (b) Zhong, Q.; Shao, J.; Liu, C.; Lu, R. Yingyong Huaxue 1991, 8, 17 (CA 1992, 116, 83 329). (c) Zhong, Q.; Lu, Y.; Liu, C.; Tao, W.; Zou, Y. Chin. Chem. Lett. 1991, 2, 683 (CA 1992, 116, 173 723).

Jean-Pierre Finet

Université de Provence, Marseille, France

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