Telluride anion

Disubstituted isotellurazoles 1 (4-11%) and bis((3-acylvinyl)tellurides 3 (3-10%) were isolated in very low yields from the reaction mixture as the products of nucleophilic addition of telluride anion to the triple bond of the initial ethynyl ketones (83S824). This method cannot be applied to the synthesis of 3//-isotellurazoles. When a-acetylenic aldehydes were used instead of ethynyl ketones, bis((3-cyanovinyl)tellurides 4 obtained in 14-20% yields were the only products (83S824). 

Actually, the greatest practical facilities, the most general applicability and the highest yield to prepare bisvinylic tellurides from elemental Te and acetylenes are achieved by using NaBH4 to generate the telluride anion. ... 

From organyl tellurolate (and telluride) anions and vinyl bromides... 

The first reported radical reaction promoted by tellurium reagent was probably the conversion of allylic halides into the coupled 1,5-dienes by treatment with telluride anions. The reaction, which gives the best results when employing the reagent prepared in situ from elemental tellurium and lithium triethylborohydride, proceeds through the intermediacy of the thermally unstable bis-allylic telluride followed by extrusion of tellurium and coupling of the formed allylic radicals. 

Whereas no other methods of synthesis of 21 and its derivatives are currently known, the nucleophilic addition of telluride anion to 1,5-diorganylpentadi-1,4-ynes may be considered a promising approach, based on the finding that sodium telluride reacts smoothly with monosubstituted alkynes, giving rise to divinyltellurides (89MI1). 

Likewise, no products of the anti-Michael addition were found in the reaction above. Compound 27 was obtained in 28% yield in the case of 1,5-diphenylpenta-l, 4-diyn-3-one (82JOC1968) when bis(ferf-butyldimeth-ylsilyl) telluride was used as the source of telluride anion. Heterocycle 22 (R1 = R2 = Ph) is also formed (in 19% yield). 

The addition of telluride anion to l-(trimethylsilyl)penta-l, 4-diyn-3-ones apparently represents a general method for the preparation of 2-substituted l-telluracyclohexa-2,5-dien-4-ones 22 (92MI3). In actual fact, the reaction of l-(trimethylsilyl)-5-phenylpenta-l,4-diyn-3-one with telluride anion affords 22 (R1 = Ph, R2 = H) in 38% yield, whereas only 12% of this compound is attained in the reaction with l-phenylpenta-l,4-diyn-3-one (87JOC3662). 

Isotellurazoles 4 were obtained in low yields (3-11%) by the one-pot reaction of alkynyl ketones with hydroxylamino-O-sulfonic acid and K2Te in aqueous solution containing sodium acetate (83S824 87H1587). A plausible mechanism of the reaction includes formation of the oxime derivative and subsequent nucleophilic addition of telluride anion to the triple bond followed by cyclization to 4. The reaction is accompanied by the formation of telluro bis(alkenyl ketones) 5 in yields approximately equal to those of 4. When alkynyl aldehydes are used instead of ketones, the single reaction products are the tellurobis(alkenyl nitriles) 6 (83S824). 

A general method of synthesis of l-hetera-4-telluracyclohexa-2,5-dienes 90 is founded in the nucleophilic addition of telluride anion to type 91 diacetylene derivatives. The telluride dianion is prepared in situ from the elements in liquid ammonia. The reaction was carried out with methanol or mixtures with DMSO and liquid ammonia as solvents, with the following diacetylenes di(l-alkynyl)sulfides (73RTC1326), I-alkynylethynyl sulfides (75RTCI63), di(l-alkynyl)sulfones (78RTC244), and di(l-alkynyl)phosphi-noxides (75RTC92). 

A number of methods developed for the preparation of tellurantrene are based on reactions stipulated by the high nucleophilicity of tellurolate and telluride anions. One such method allowing the preparation of tellurantrene in 50-60% yield employs coupling benzene-1,2-ditellurolate (see Section III,H, 1) with 1,2-diiodobenzene (90KGS137 91KGS1203). 

Radical accumulators whose presence might facilitate addition to / -mono and / ,/ -disubstituted olefins were conceived. It seemed to us that alkylaryl or dialkyl tellurides should react with alkyl radicals and give an intermediate radical of type R1R2R8Te (an expanded valence shell) which might have a relatively longer life on the radical time scale. A secondary objective would be the exchange of one radical against another. In this way, the special nucleophilic properties of the aryl telluride anion for example, could be exploited to make complex natural product derived radicals. 

When aromatic nitro compounds were reduced in dimethylformamide with disodium telluride to aza derivatives, bis[dimethylaminocarbonyl ditellurium was obtained in 5 to 15% yield as a by-product. The formation of this ditellurium compound was attributed to the capture of a telluride anion by a dimethylcarbamoyl radical and subsequent oxidation of the tellurocarbamoyl species5. 

The sodium borohydride method appears to be the most convenient and most widely applicable route to dialkyl telluriums. Sodium dithionite was also used to prepare disodium telluride11, which subsequently was reacted with methyl, ethyl, propyl, and pentyl halides. Tellurium was also electrochemically reduced to the telluride anion in an ultrasonically aided reaction15 using tellurium powder in acetonitrile, and to the tetratelluride dianion with a tellurium rod as cathode and sodium perchlorate in dimethylformamide as electrolyte16. 

A few reactions were carried out that proved that the telluride anion adds to carbon-carbon triple bonds. The corresponding diorgano telluriums were obtained in low yields. Tellurium, when heated with acetylene, water, and a base, produced divinyl tellurium. Telluride was claimed to be a product of the disproportionation of tellurium3. When this reaction was carried out with aqueous potassium hydroxide and hexamethylphosphoric triamide at 120° in a steel autoclave under 10 atm acetylene, the yield of divinyl tellurium was 30%4. The yield increased to 94% when tin(II) chloride was present in the reaction mixture5 1. 

The ditellurium compounds, in which a Te —Te group joins two carbonyl groups, can be considered to be the tellurium analogs of peroxy compounds derived from carbonic acid or benzoic acids (e.g. benzoyl peroxides). Only a few of these compounds are known. During the reduction of aromatic nitro compounds with disodium telluride in dimethylfor-mamide, bis[dimethylaminocarbonyl] ditellurium was formed as a by-product in yields from 5 to 15%. The formation of this compound was attributed to the capture of the dimethylaminocarbonyl radical by the telluride anion and subsequent oxidation of the tellurocarbamoyl species4. 

On the other hand, polytellurides only seem to oxidize metals to the +1 or +11 state. Reaction of equimolar amounts of Te4 with M(CO)6 results in disubstitution of CO forming a cu-complex (CO)4MTe4 (M = Cr (45), W (47)47). If an excess of metal carbonyl is used in the presence of poly-telluride anion, multinuclear products can be isolated and metal-metal bonds can also form, leading to clusters. Careful manipulation of reaction conditions and choice of the polychalcogenide anion used makes possible partial oxidation of the metal centers and cluster formation. The reaction of iron carbonyls with polytelluride anions can lead to a wide array of cluster compounds, the identities of which are controlled by the stoichiometries and compositions of the starting telluride anions. For instance, reaction of [Fe(CO)5] with Te2 leads to the formation of [Fe3(CO)9(ju.3-Te)]2 (48),48 whereas its reaction with increasing amounts... 

The telluride-anions are sufficiently nucleophilic to react also with aryl halides to afford aryl tellurides, but generally the aryl group must be activated either by an additional substituent, or the reaction must be carried out at higher temperatures. For example,j9ara-iodobenzene reacts at 110-120 °C with sodium telluride to form polymeric poly-/ -phenylenetelluride. ... 

Telluriranes were postulated as intermediates in the conversion of 2-R-2-chloromethyl-oxiranes by telluride anions to allyl alcohols. ... 

The reaction can be rationalized as involving an E2 fragmentative attack by the telluride anion at the halogen atom. Sodium hydrogen telluride (method B) requires a shorter reaction time than sodium telluride (method A), the 2-bromoalkyl esters reacting very rapidly. Sodium hydrogen selenide reacts similarly but more slowly. ... 

The synthesis of l(7)-menthene-2,8-diols (655) has been mentioned (Vol. 4, p. 526, Ref. 503) the two isomers have now been isolated from Osmitopsis asteriscoidesThe known acetate 656, an insect repellent, has been isolated from Mentha haplocalyx oil, and a review of synthetic methods has been published by Verghese. In this connection, attention is drawn to a method for reducing an epoxide in the presence of a ketone, by reaction with phenyl telluride anion, PhTe, then triphenyltin hydride. The dihydrocarvone epoxides (657) yielded the hydroxy dihydroketone 658 corresponding to 656. Note also... 

Telluride anions have been known for a hundred years. Presently about 200 binary tellurides have been synthesized and there are ca. 50 species that have been structurally characterized. Their synthetic and structural chemistry as well as their ligand properties and applications have recently been reviewed several times. 

Due to their easy access from haloalkane derivatives, the chemistry of 2,3,4,5-tetrahydro-tellurophenes and l,3-dihydrobenzo[c]tellurophene is very well document (see above). Improvements upon the nucleophilic character of the telluride anion were made either by the use of tin telluride <90TL6291> or by use of phase transfer catalysis conditions <89SRI931>. 

The telluride anion also adds to triple bonds to give tellurophene derivatives. With the... 

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