[65829-99-4] · Cl4Te · Tellurium(IV) Chloride · (MW 269.40)
(for carbon-carbon bond-forming reactions and functional group manipulation via telluration; Lewis acid for thioacetalization/deacetalization and rearrangements; chlorinating agent)
Physical Data: mp 224 °C; bp 390 °C/755 mmHg; d 3.01 g cm-3.
Solubility: insol cyclohexane, hexanes, methylene chloride, chloroform; sol acetonitrile, DMSO, DMF; slightly sol ether, benzene.
Form Supplied in: pale yellow solid; widely available.
Purification: distillation, or, more conveniently, sublimation (200 °C/0.1 mmHg).
Handling, Storage, and Precautions: readily hydrolyzed by water and must be handled and stored in the absence of moisture. The toxicity of tellurium and organotellurium compounds is little investigated. Use in a fume hood.
Many aromatic compounds undergo electrophilic aromatic substitution with TeCl4 to yield aryltellurium trichlorides and diaryltellurium dichlorides.2 These compounds can be converted into symmetrical biaryls by treatment with degassed Raney Nickel in high-boiling ether solvents (eq 1).3,4 On treatment with Tetracarbonylnickel5 or Carbon Monoxide in the presence of a palladium(II) salt,6 the organotellurium compounds are carbonylated to give benzoic acid derivatives. When TeCl4 is allowed to react with four equiv of 1-alkynyllithium reagents, 1,3-diynes are formed,7 probably via reductive coupling8 from intermediate tetrakis(1-alkynyl)tellurium species.
Tellurium(IV) chloride readily adds to a variety of alkenic substrates to produce b-chloroalkyltellurium trichlorides. In the presence of a radical scavenger, the addition is highly syn specific.9 The anti specific Sodium Sulfide-induced elimination of tellurium from this compound has been used for the mild inversion of alkenes (eq 2). TeCl4 undergoes a diastereospecific 1,3-addition to a-substituted allylic esters with 1,2-migration of the acyloxy group.10 After hydrodetelluration (Raney Ni) and alkaline hydrolysis/ring closure of the resulting chlorohydrin ester, epoxides are formed (eq 3).
The reaction of alkenes with TeCl4 and lithium acetate in acetic acid at 120 °C affords products of syn diacetoxylation of the double bond.11 This reaction probably proceeds via anti acetoxytellurination followed by acetate-induced cleavage of the C-Te bond with inversion of configuration. The replacement of an alkyl-, alkenyl- or aryl-bound TeCl3 group by chlorine can be induced by heat, light, or oxidation to give cis-1,2-dichloroalkanes, cis-1,2-dichloroalkenes, and aryl chlorides, respectively.12
Aldehydes and ketones react with alkanethiols in the presence of a catalytic amount of TeCl4 to form dithioacetals in good yields. In the presence of a stoichiometric amount of the tellurium reagent, dithioacetals and acetals are easily cleaved by the reagent to regenerate the carbonyl compounds (eq 4).13,14
When the deprotection procedure is applied to five-membered cyclic thioacetals, a facile ring enlargement takes place to give a dihydro-1,4-dithiin.15 TeCl4 catalyzes the oligomerization of phenylethylenes and benzyl chlorides.16 Cycloheptatrienes undergo rearrangement with chlorination to give benzyl chlorides in the presence of TeCl4.17 Alcohols are converted to the corresponding alkyl chlorides when treated with TeCl4 in nonpolar solvents. In aromatic solvents, the tellurium compound acts as a Friedel-Crafts catalyst to give alkylbenzene derivatives.18 When treated with TeCl4, silyloxycyclopropanes afford b-oxyalkyltellurium trichlorides in high yields.19 On treatment with Dimethyl Sulfoxide or amine bases, dehydrotelluration occurs to give a-methylene ketones (eq 5).
Unsaturated or halogenated cyclic or polycyclic hydrocarbons are readily aromatized when heated with TeCl4 at elevated temperature (ca. 80 °C).20 Chlorinated intermediates were proposed in the reaction. Aromatic compounds are chlorinated by TeCl421 and b-ketonitroalkanes are both chlorinated and partly deoxygenated to give a-(hydroxyimino)-a-chloro ketones. The nitriloxides resulting from the latter compounds react with stilbenes to form isoxazolines.22 It has been reported that the formation of oxamide derivatives, RNHC(O)C(O)NHR, from isocyanides, RNC, in the presence of TeCl4 involves initial insertion of the isocyanide into the Te-Cl bond.23
Uppsala University, Sweden