Cyclic tellurides

Cyclic tellurides, including some with a steroidal structure, - have been prepared by the Rongalite method. 

As a cyclic telluride, tellurachromanone is prone to oxidative addition reactions which increase the coordination number of the tellurium atom to 3 or 4 (90UP1). Under mild conditions tellurachromanone adds halogens,... 

Synthesis of the racemic cyclic telluride (2,7-dihydro-17/-dinaphthoR,i ]tellurepin 78), possessing a C2 axis, was based on the reaction of 2,2 -bis(chloromethyl)-l,10-binaphthalene 109 with potassium tellurocyanate in dry DMSO. Reaction of 109 with iodide gave the diiodo derivative (Scheme 7) <2004JOM(689)2377, 1996RTC427>. 

The iodo-formates obtained as described above are useful intermediates, which can be further transformed into cyclic amines, cyclic sulfides, cyclic tellurides, and cyclic selenides by the sequences outlined in Scheme 49. A variety of heterosteroids have been synthesized from the corresponding steroidal... 

Data on the electrochemistry of the telluride ion in alkaline media are relatively limited. Mishra et al. [53] studied the oxidation of Te to Te° at solid electrodes, focusing on the intermediate step(s) of this process, and in particular, the possibility of detecting ditelluride Te via rotating ring disk electrode (RRDE) methodology. Oxidation beyond the elemental state to TeO and TeO was also studied using cyclic and hydrodynamic voltammetry. 

The electrodeposition of tellurium and silver has been investigated in dilute aqueous solutions of tellurous acid and Ag " ions (concentrations in the order of 10 to 10 " M) in 0.1 M HCIO4 [164], In particular, cyclic voltammetry experiments were conducted with rotating glassy carbon disk electrodes in baths with various concentration ratios of Ag(I) and Te(IV) precursors, and their outcome was discussed in terms of the voltammetric features. For a Ag(I)/Te(IV) ratio close to 0.8, formation of quasi pure silver telluride, Ag2Te, was reported. The authors, based on their measurements and on account of thermodynamic predictions, assumed that silver is deposited first on the electrode (Ag" + e Ag), and then Te(IV) is reduced on the previous silver deposit with formation of Ag2Te according to the reaction... 

Menke EJ, Brown MA, Li Q, Hemminger JC, Penner RM (2006) Bismuth telluride (Bi2Te3) nanowires Synthesis by cyclic electrodeposition/stripping, thinning by electrooxidation, and electrical power generation. Langmuir 22 10564-10574... 

Attempts to synthesise tritellurophosphonic acids or their salts have so far proved unsuccessful, and synthetic routes from primary phosphines analogous to Equation 39 with E = Te give just cyclic polyphosphanes (RP) and lithium telluride with no observed tritellurophosphonate formation.45... 

As an alternative to hydrozirconation of acetylenic tellurides or selenides, Dabdoub and co-workers have more recently described the first additions of the Schwartz reagent (one equivalent) to acetylenic selenide salts 51 (Scheme 4.30) [52]. Subsequent alkylation at selenium produces 1,1-dimetallo intermediates 52, which are cleanly converted in a one-pot process to stereodefined products 53. It is noteworthy that ketene derivatives 52 are of ( )-geometry, the opposite regiochemistry to that which results from hydrozirconation of acetylenic tellurides (vide supra). This new route also avoids the mixtures of regio-isomers observed when seleno ethers are used as educts. The explanation for the stoichiometric use of Cp2Zr(H)Cl in these reactions, in contrast to the requirement for two equivalents with seleno ethers, may be based on cyclic intermediates 54, in which Li—Cl coordination provides an additional driving force. Curiously, attempted hydrozirconation of the corresponding telluride salt 55 under similar conditions was unsuccessful (Scheme 4.31) (Procedure 12, p. 143). 

When the alkylating agent is insoluble in liquid ammonia, as in the case of long-chain compounds, an organic solvent is added to the sodium telluride residue after evaporation of the ammonia. Some cyclic and steroidal tellurides have been prepared from sodium telluride in ethanol and the appropriate dihalides. ... 

Aryltellnrinyl acetates, generated as previously described from the corresponding tellurinic anhydrides and acetic acid, add to hydroxy olefins, giving tellurinylated cyclic ethers. The reaction is performed in refluxing acetic acid or in chloroform in the presence of BFj EtjO. Owing to their hygroscopicity and intractable nature, the products are reduced with hydrazine hydrate, and isolated as tellurides (as for the aminotellurinylation reactions). 

In accordance with the following scheme the hydroxyaldehyde A was submitted to a Wittig olefmation followed by the mesylation of the hydroxyl group to give the a,)3-unsat-urated compound B which was in turn converted into the telluride C by treatment with the appropriate aryltellurolate. Irradiation of C in the presence of iV-acetoxy-2-thiopyridone gave rise to the cyclic compound D. 

Trithiolane is a stable compound at room temperature, although it will polymerize eventually and is best kept cool and sealed from the atmosphere. Separation of cisjtrans mixtures of 3,5-dialkyl-1,2,4-trithiolanes is possible on alumina. Reverse-phase HPLC has been used to separate cyclic methylene sulfides, and tellurides with retention times and capacity factors dependant in a systematic way on ring size, number and type of chalcogens and the number of heteronuclear bonds within the ring. 

The ring system embodied in these cyclic derivatives is produced by condensing aluminium telluride with ae-pentamethylene dibromide ... 

The D-tf//o-inositol-based cyclic sulfate 53 has been reduced with sodium hydrogen telluride to the protected conduritol (Equation 13) <2000EJ01285>. 

Reduction of cyclic tellurium oxychloride 22 with stoichiometric amounts of sodium borohydride or excess sodium bisulfite yields the telluride 56, whereas treatment with a great excess of sodium borohydride quantitatively leads to di-/>-methoxyphenyl ditelluride and alkyne 57 (Scheme 6) <1999OM803>. 

The reaction of 1,2-diiodoacenaphthene (334) with Na2Te in DMF at room temperature gave the cyclic bis-telluride (335) in 35% yield (equation 198)301. 

Reaction of tellurium tetrachloride with substrates bearing an internal nucleophile 20 gives rise to cyclic products.66,67 In some cases, the organotellurium trichlorides 21 obtained in this way are reduced to the corresponding organotellurolates 22 followed by alkylation to give tellurides 23 (Scheme 6).47... 

Reaction of 116 with monosubstituted aryl alkynes 120 gives the (Z)-vinylic aryltellurium dichlorides 121, which are reduced to the (Z)-vinyl aryl tellurides 122 by reaction with sodium boro hydride.185 Alkynes bearing an OH at C3 react with aryltellurium trichlorides 116 to give cyclic products 124 or 125 depending on the steric demand on C3, in a similar way that was observed in the reaction with tellurium tetrachloride (Section 9.13.4.2.3). 

The following cyclic tellurium compounds were prepared from sodium telluride in ethanolic solution and the appropriate organic dihalides ... 

Chloro-3-cyano-4,6-diphcnylpyridinc reacted with sodium hydrogen telluride in ethanol under an argon atmosphere to produce a cyclic telluronocarboxylic amide (tellurolocar-boxylic imide)1. 

Hydroxyethyl)cyclopent-l-ene and benzenetellurinyl acetate formed an addition product containing a cyclie-ether functionality. This intermediate was reduced to the telluride, the telluride converted to the tellurium dibromide, and the dibromide heated in dimethylformamide with sodium bromide to give the brominated cyclic ether5. 

Reaction of cyclic sulfates or thionocarbonates, derived from 1,2-diols, with telluride results in stereospecific alkene formation <1995TL7209>. This is illustrated by the conversion of the cyclic sulfate OTitra-l,2-diphenyl-l,2-ethanediol 49 into fif-stilbene exclusively by Te, as shown in Equation (13). Treatment of the cyclic sulfate of 47-1,2-diphenyl-1,2-ethanediol with Te produces /ra r-stilbene exclusively. These results are accounted for by intermolecular Te Sn2 displacement followed by intramolecular Sn2 displacement to form the corresponding tellurirane. The tellurirane then thermally loses tellurium stereoselectively forming alkene. Cyclic sulfates need not be used dimethanesulfonates or di-/i-toluenesulfonates prepared from 1,2-diols also, stereospecifically, provide alkenes via telluriranes <1993CC923, 1996SL655>. 

The diaryl telluride, alkyl aryl telluride, and dialkyl telluride carrying sulfopropyl groups were prepared and were found to be the most efficient tellurium based inhibitors of thioredoxin reductase ever tested. The results clearly showed that of the four cyclic aryl alkyl chalcogenides 162-165, all primitive analogues of vitamin E, only the tellurium compound, 165, showed interesting inhibition characteristics. 

The cyclic structure of tellurenyl halides 2 stabilized by an intramolecular coordination 0->Te bond provides for their peculiar reactivity unusual for tellurenyl halides without such a bond. Whereas reduction of the latter gives diaryl ditellurides (99ZOK981), 2 under the same condititions are transformed into /u. v(2-aroylvi-nyl)tellurides 21 (in more than 80% yield), ditellurides 22 being formed as a minor product (86JOC1692) (Scheme 11). 

The difference in stability between the cyclic six- and seven-membered methoxy tel-luroxides is noteworthy. Indeed, while the cyclohexane derivative is stable and isolable, giving ring contraction on treatment with 1 equiv of MCPBA, the cycloheptane derivative is unstable, suffering telluroxide elimination (like cycloheptene formation from cyclohep-tyl phenyl telluride), as will be shown in Section 4.7. 

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