Dibutyl telluride

Elemental tellurium can be recovered from dibutyl telluride by the following procedure. Under nitrogen, naphthalene (4.0 g) and dry THF (100 mL) are placed in a... 

Dibutyl telluride (typical procedure) Hydrazine hydrate 80% (0.50 ml., 7.1 mmol) is added dropwise using a syringe to a stirred mixture of finely ground Te (0.64 g, 5 mmol) and powdered NaOH (0.40 g, 10 mmol) in DMF (10 mL) at 50-60°C. After 3 h stirring, n-butyl bromide (1.4 g, 10 mmol) in DMF (2 mL) is added, the mixture is heated at 60°C for a further 30 min, cooled at room temperature and extracted with petroleum ether (40-60°C). The organic phase is separated, washed with HjO, dried (CaClj) and evaporated, giving the pure telluride (0.69 g (57%) b.p. 111-114°C/13 torr). 

Dibromomalonates react with aldehydes under the assistance of dibutyl telluride (2 equiv) to afford alkylidene malonates. ... 

Otherwise, dibromomalonates (and nitriles) react with a-unsaturated carbonyl compounds in the presence of only 1 equiv of dibutyl telluride, giving cyclopropane derivates. 

Cyclopropanation of a,fi-unsaturated carbonyl compounds with dibromomalonates (typical procedure) To a mixture of diethyl dibromomalonate (0.95 g, 3 mmol) and methyl vinyl ketone (0.27 g, 3.1 mmol) is added dibutyl telluride (0.73 g, 3 mmol) under argon and with stirring. The exothermic reaction is completed within 1 h. The mixture is chromatographed on an AI2O3, column (70-230 mesh, elution with EtOAc), giving dibutyltellurium dibromide (1.01 g, 84%) and then l-acetyl-2,2-bis(ethoxycar-bonyl)cyclopropane, which is purified by Kiigelrohr distillation (0.59 g (86%) b.p. 88-90°C/0.08 torr). 

In the presence of dibutyl telluride, iodomethyl triphenylphosphonium iodide reacts with aldehydes, in accordance with a Wittig-type olefmation, giving methylenation products. ... 

Methylenation reaction (typical procedure) A mixture of iodomethyl triphenylphosphonium iodide (0.530 g, 1.0 mmol), dibutyl telluride (0.242 g, 1.0 mmol) and p-bromoben-zaldehyde (0.096 g, 0.5 mmol) in THF (5 mL) is heated under reflux for 30 h, then cooled and filtered. The residue is purified by TLC, giving p-bromostyrene (0.080 g (87%)). 

Catalytic one-pot procedure. Since in the described teUuronium ylide olefmation tellurox-ide is formed as a by-product, and the telluroxide is susceptible to reduction by triphenyl phosphite, a catalytic procedure can be employed, providing a practical one-pot synthesis of a, -unsaturated esters and ketones (method E). By this procedure, a catalytic amount of n-dibutyl telluride reacts with the a-bromoester or a-bromoketone, and the formed tel-luronium salt is converted in situ under phase transfer conditions (solid KjCOj/trace HjO) into the ylide, which reacts in turn with the aldehyde, giving the olefin. Since the reaction is performed in the presence of triphenyl phosphite, the formed dibutyl telluroxide is reduced back to the dibutyl telluride, which is then recycled. 

Method D - using dibutyl telluride (typical procedure). A mixture of 3-nitrobenzalde-hyde (0.38 g, 2.5 mmol), methyl bromoacetate (0.38 g, 2.5 mmol) and dibutyl telluride (0.61 g, 2.5 mmol) is refluxed in THF. After 6 h, the mixture is worked up as for method C to give pure ( )-methyl 3-(3 nitrophenyl)propenoate (0.460 g (89%)). 

Method E - catalytic procedure (typical procedure). Benzaldehyde (106 mg, 1.0 mmol), methyl bromoacetate (165 mg, 1.1 mmol), triphenyl phosphite (356 mg, 1.2 mmol), dibutyl telluride (48 mg, 0,2 mmol), KjCOj (179 mg, 1.3 mmol) and THF (4 mL) are mixed and stirred at 50°C for 13 h (monitored by TLC). The reaction mixture is filtered rapidly through a small amount of SiOj with EtOAc as the eluent to remove inorganic salts and dibutyltellurium oxide. Preparative TLC with EtOAc/petroleum ether at 60-90°C (1 9) as the eluent yields 3-phenylpropenoate (160 mg (98%)). 

Te-Li exchange in bis(2-arylethenyl)tellurides (run 15). To a solution of bis-[2-(p-tolyl) ethenyl] telluride (0.361 g, 1 mmol) in THE (4 mL) at -78°C under nitrogen, a solution of n-BuLi (0.91 mL, 2.1 mmol, 2.42 M solution in hexane) was added dropwise. After 20 min of stirring at this temperature, DMF (0.2 mL, 2.58 mmol) was added. The temperature was raised to room temperature and stirred for 1 h, then diluted with ethyl acetate (30 mL) and washed with water (3x10 mL). The organic layer was separated, dried with MgS04 and the solvent removed under vacuum. Elution with hexane removed dibutyl telluride, and elution with ethyl acetate gave a low-m.p. solid. Yield 0.175 g, 60% (characterized as the semi-carbazone m.p. 108.4-109.4°C). 

From the point of view of the hetero-atom itself, there are two more known below selenium in the Periodic Table. Each deserves some special comment. The next atom, directly below selenium, is tellurium. It is more metallic, and its compounds have a worse smell yet. I heard a story about a German chemist, many years ago, who was carrying a vial of dibutyl telluride in his pocket in a passenger coach from here to there in Germany, back at about the turn of the century. It fell to the floor and broke. No one could remain in the car, and no amount of decontamination could effectively make the smell tolerable. Scratch one railway coach. But the compound, 2C-TE, would be readily makeable. Dimethyl ditelluride is a known thing. 

Dibutyl telluride 59 reacts with iodomethyl triphenylphosphonium iodide to give triphenylmethylidene phosphor-ane, which reacts with aldehydes leading to the methylenation products in good yields.119 The same reagent 59 also assists the reaction of dibromomalonates 60 with aldehydes and activated olefins affording alkylidene malonates 61 and cyclopropanes 62 derivatives, respectively (Scheme 30). 

Cyclopropanes 1,1,2-trisubstituted with electron-withdrawing groups are prepared by treating electron-deficient alkenes with dibromomalonic ester or related active methylene dibromides in the presence of trialkylstibine (equation 132)) dibutyl telluride or... 

Stabilized telluronium ylides such as dibutyltelluronium carbethoxy, phenacyl/ cyano- and carbamoylmethylide (easily prepared by the reaction of dibutyl tellurides with the appropriate substituted methyl halides, followed by treatment with a base), undergo Wittig-type olefmation reactions with a variety of carbonyl compounds, giving the expected olefins in satisfactory yields (method A). This behaviour is in sharp contrast to that of stabilized sulphonium yhdes, which are inert towards carbonyl compounds. 

The reaction of dibenzotellurophene with butyllithium causes the opening of the tellurophene ring and gives 2,2 -diphenyllithium and dibutyl telluride the kinetics of the reaction has been discussed.93... 

We add an investigation of Chinese chemists to this section, although it is not related to carbenoid reagents that we have discussed above. Zhou et al. (1993) studied reactions of dimethyl diazomalonate and ethyl diazoacetate with carbonyl compounds mediated by diorganyl tellurides and catalytic amounts of cuprous iodide (8-69). Dibutyl telluride (8.155) yields the dimethyl l-arylethene-2,2-dicarboxylate 8.157 with 4-chlorobenzaldehyde in 95<7b yield at 100 °C. It is assumed that the reaction passes the telluronium ylide 8.156 as intermediate. If so, the process is clearly different from the carbenoid transformations discussed in this section. The originally diazo-substituted C-atom has nucleophilic character in 8.156 and is not electrophilic, as in 8.104. 

When BuLi was added to aryltellurol esters in THF/Et20 at low temperatures in the presence of pinacolone as an electrophile, a-hydroxy ketones 90 were obtained in high yields via aroyllithiun 89 together with dibutyl telluride (Eq.66) [124]. 

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