Arene-catalyzed lithiation

Allylic and benzylic ethers can also be cleaved using an arene-catalyzed lithiation, so the corresponding organohthium intermediates could be generated. Thus, different benzylic ethers 49 were hthiated using a catalytic amount of naphthalene (5%) to yield the expected intermediates 50, which after reaction with electrophiles and final hydrolysis gave products 51 (Scheme 16) . ... 

As shown in the last section, the arene-catalyzed lithiation of mesylates has the limitation that it only proceeds for allylic and benzylic substrates. This drawback has been... 

Although the most important reaction of rednctive carbon-snlfnr bond cleavage involves alkyl phenyl thioethers, arene-catalyzed lithiation has also been studied using other snlfnr-containing componnds, snch as thiols, disnlhdes, snlfoxides and sulfones. 

Oxido functionalized organolithium compounds of type 128 or 131 are also accessible by sulfur-lithium exchange using the arene-catalyzed lithiation technology. 

Lithium homoenolates derived from carboxylic acids were generated from the corresponding /3-chloro acids by means of an arene-catalyzed lithiation. Chloro acids 186 were deprotonated with n-butyllithium and lithiated in situ with lithium and a catalytic amount of DTBB (5%) in the presence of different carbonyl compounds to yield, after hydrolysis, the expected hydroxy acids (187). Since the purification of these products is difficult, they were cyclized without isolation upon treatment with p-toluenesulfonic acid (PTSA) under benzene reflux, into substituted y-lactones 188 (Scheme 64) . 

In this section, functionalized aryl and heteroaryl compounds prepared by arene-catalyzed lithiation will be considered. 

The preparation of functionalized aryllithium compounds bearing an oxygen- or sulfur-containing functionality in a benzylic position is also possible by arene-catalyzed lithiation. When chlorinated materials 239 were deprotonated (for Y = OH, SH) with n-butyllithium in THF at —78 °C and then lithiated using DTBB as the catalyst at the same temperature. 

Six-membered heterocycles are more resistant to an arene catalyzed lithiation than the corresponding five-membered ones. For instance, tetrahydropyran can not be cleaved under the reaction condition employed to open tetrahydrofuran (activation by BF3) ... 

Concerning the arene-catalyzed lithiation of 4-77-chromene 386, the process is not of synthetic interest as compared to the same process applied to 2,3-benzofuran 348 because both alkyl-and aryl-oxygen cleavage took place using DTBB (5%) as the electron-carrier... 

Dioxanes can be opened by an arene-catalyzed lithiation only if the carbon-oxygen bond to be cleaved occupies an allylic or benzylic position. This is the case of the vinyl-dioxane 416, which reacted with lithium and a catalytic amount of DTBB in THE at 0 °C, and the allylic intermediate 417 generated reacted at the y -position with tridecyl iodide to yield the compound 418, used in the synthesis of plasmenyl-type lipids (Scheme 117) . 

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