Tellurides tellurium-lithium exchange

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... 

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... 

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... 

Table 5 Tellurium-copper exchange of vinylic tellurides with lithium cyanocuprates...

Lithium-tellurium exchange generation of vinyllithium (typical procedure). Method A. To a solution of butyl vinyl telluride (0.211 g, 1 mmol) in THF (4 mL) at -78°C under N2 is added dropwise a solution of n-BuLi (1.5 M in hexane, 0.67 mL, 1 mmol). After stirring for 40 min at -78°C, benzaldehyde (0.016 g, 1 mmol) is added. The mixture is allowed to react at room temperature for 30 min, diluted with EtOAc (40 mL) and washed with brine. 

Tellurides 1129 prepared from a-bromo-o-toluylesters 1128 undergo lithium-tellurium exchange to give the corresponding benzylic anions 1130, which react with aldehydes or ketones to afford dihydroisocoumarins in high yield (Scheme 281) <1997SL1047>. 

By treatment of diorganyl tellurides with alkyUithiums in THF at -78°C, a lithium-tellurium exchange occurs, generating anomer organohthium if me latter is more stable man me former. 

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