Tellurium-lithium exchange

Tellurium-lithium exchanges in the mono- and bis-telluroderivatives are a suitable route for the preparation of mono- and disubstituted ferrocenes. ... 

Bis(lithiomethyl) sulphane (99) is also accessible by tellurium-lithium exchange reaction, when reacting bis(butyltelluriomethyl) sulphane (112) with two equivalents of n-butyllithium in diethyl ether. Two equivalents of dibutyltellurium are cleaved off in this reaction (Scheme 40). 

Tellurium-lithium exchange in cyclic systems, like the telluranaphthalene 120, has been demonstrated by Sashida. The possibility of a two-fold tellurium-carbon bond cleavage introduces a route to doubly hthiated compounds. When compound 120 is treated with an excess of n-butyllithium in THF, the lithiated lithium tellurate 121 is formed, which is interconverting to the doubly hthiated compound 122 (Scheme 44, verified by deuteriolysis). 

For the hthiation reactions of the closely related compound 123 with w-butyllithium, a significant solvent effect was observed by Maercker and coworkers . While a two-fold lithiation process by tellurium-lithium exchange takes place in hexane, yielding highly pyrophoric 91, only a-deprotonation occurs when the reaction is effected in THF, yielding the monohthiated tellurole 124 (Scheme 45). 

In a rather more unusual process, presumably involving tellurium-lithium exchange, acyl tellurides may be converted into silyl enol ethers of acyl silanes by treatment with butyl lithium and trimethylchlorosilane. In this procedure it is the Z isomer which is the predominant product (Scheme 24)100. 

The method is less successful with benzylic and allylic halides, and problems of selectivity with these substrates have been overcome in the past via an initial substitution with lithium butyltelluride the organolithium is then formed cleanly from the telluride 135 or 136 (which need not be isolated) by tellurium-lithium exchange.112... 

A similar stable stannolate 160 was produced on attempted transmetallation of benzostannole 159, itself produced by tellurium-lithium exchange from 158.131... 

Tellurium-lithium exchange proceeds in much the same way as selenium-lithium exchange but is rarely used.144 Vinyltellurides such as 179 can be converted stereospecifically into vinyllithiums 180,145 and alkyltelluro-heterocycles have been used as precursors to lithio-species.146... 

There is one important class of exchange which is unique to tellurium telluroesters such as 181 undergo tellurium-lithium exchange to generate the highly unstable acyllithiums such as 183.147 These must be formed in the presence of an electrophile - typically pinacolone (t-butyl methyl ketone 182) or they decompose. 

The tellurium-lithium exchange is one of the fastest lithium-metalloid exchange reactions.238 Recently, NMR studies provided evidences that this exchange proceeds through an ate complex.239... 

Several years ago, Seebach described the tellurium-lithium exchange reaction of bis-(phenyltelluro)-methane 148 with an alkyllithium. The phenyltelluromethyllithium 149 formed was captured with electrophiles (Scheme 89).241... 

Table 3 Tellurium-lithium exchange reactions of organic tellurides...

Recently, substituted aromatic tellurides were submitted to the tellurium-lithium exchange reaction as a way to access substituted aryllithiums,48 synthetic intermediates normally prepared by halogen-lithium exchange. Alkyltelluro heterocycles were also successfully transformed into lithium heteroaromatics.246 247... 

The tellurium-lithium exchange reaction of functionalized alkyl tellurides is described. A / -(butyltelluro)-ketal is prepared in situ and then reacted with -butyllithium to give the corresponding functionalized alkyllithium 157, which is captured with electrophiles (Scheme 92).250... 

To our knowledge, the first example reported of a tellurium-lithium exchange reaction leading to a vinyllithium was the reaction of 2,5-diphenyltellurophene 165 with -butyllithium, giving l,4-dilithium-l,4-diphenylbuta-l,3-diene 166, which was trapped with several electrophiles leading to the corresponding disubstituted dienes 167 with retention of configuration (Scheme 95).254... 

Kauffmann reported the first tellurium-lithium exchange reaction of a vinylic telluride with an organolithium compound.255 Phenyl vinyl telluride 168 was deprotonated by lithium dicyclohexylamide (LDCA) in THF, and the resulting vinyl anion 169 was reacted with chlorotrimethylsilane to give telluride 170. Vinylsilane telluroacetal 170 was then reacted with phenyllithium to give the corresponding vinyllithium, which was captured with chlorotrimethylsilane to give the bis-silylated ethane 171 (Scheme 96).255... 

In 1987, Sonoda and co-workers reported that the tellurium-lithium exchange reaction of l-(phenyltelluro)-2-phenylethene with -butyllithium, followed by capture with benzaldehyde, gave the corresponding allylic alcohol with retention of the double-bond configuration.243 It was observed that, depending on the length of time the reaction mixture of the aryl vinyl telluride and -butyllithium was allowed to equilibrate prior to addition of the electrophile, a complex mixtures of products could be formed (Scheme 97).256... 

Table 4 Stereospecific tellurium-lithium exchange in vinylic tellurides ...

Representative examples of these reactions are shown in Table 4. For more details, see recent reviews.8 10 Recently, more complex unsaturated systems were subjected to the tellurium-lithium exchange reaction.137,141 In Scheme 98, some examples of such a process are shown. In all cases, the (Z)-stereochemistry of the starting vinylic telluride was preserved.137... 

A hydrotelluration reaction, followed by a tellurium-lithium exchange, was used in the first step of the total synthesis of Gymnodimine 182 (Scheme 100).257... 

The tellurium-lithium exchange used in the case of acyllithiums58 was also assayed for carbamoyllithiums 118, prepared by reaction of dialkylcarbamoyl chlorides with lithium n-butyltellurate111, m. The corresponding dialkylcarbamoyllithiums were prepared with n-butyllithium at —78 °C and trapped with different electrophiles including acyl chlorides and methyl vinyl ketone, which suffered conjugate addition (Scheme 31). 

Alkyl organo tellurium compounds, prepared from alkane- or arenetellurolates and alkyl halides, react with butyl lithium,. 9ec-butyl lithium, /ert.-butyl lithium, or phenyl lithium. The alkyl group bonded to the tellurium atom is cleaved from the tellurium and is present in solution as the alkyl lithium that can be used for further reactions. This tellurium-lithium exchange reaction is synthetically useful, whenever the alkyl halides cannot be converted to alkyl lithiums by other, more conventional halogen exchange reactions. The following exchange reactions were successfully carried out ... 

Enol silyl ethers of acylsilanes. On treatment with butyllithium and trimethyl-silyl chloride, these compounds undergo enol silylation, tellurium-lithium exchange, and O — C silyl migration. The lithium enolates are further silylated. 

One is the synthesis of 3,4-unsubstituted siloles 8 from the corresponding tellurophenes 7 via the well-documented tellurium-lithium exchange reaction, as shown in Scheme 3 [12]. A variety of... 

Furthermore, aldehyde reacts with the ate complex. Then the reaction product of the aldehyde with the organolithium compound, which is produced by tellurium lithium exchange reaction, is produced [80]. These reactions are applied for a... 

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