Reductive lithiation of phenyl sulfides

So far we have considered sulfur-containing carbanions obtained by metallation with appropriate bases of a to sulfur atom(s) acidic C-H bonds. For synthetic purposes this method has been by far the most used. Among the variety of other routes to such carbanions [203] we shall consider two methods which seem to be general and promising the reductive lithiation of phenyl thioethers and the thiophilie addition of organometallics to thiocarbonyl compounds (vide infra Section 4.1.2). 

The cleavage of alkyl phenyl sulfides by naphthalenelithium or a lithium dispersion in THF to afford alkyllithium reagents has been studied initially by Screttas and Micha-Screttas [309,310) as part of their hydrolithiation of a-olefins process. They prepared primary, secondary and tertiary alkyllithium reagents in fair to good yields, as shown by carbonation. 

The use ot reductive lithiation to prepare a carbanion from a dithioacetal is due to Cohen [311]  

His group [312,313] has done important work on the reductive cleavage of the C-S bonds of phenyl thioethers. These workers have shown the potential of two radical anions lithium p.p -di-t-butylbiphenylide (LDBB) and lithium l-(dimethylamino)naphthalenide (LDMAN) as reducing species. 

A wide variety of organolithium reagents have been prepared by this reductive metallation, a number of which take advantage of the complementarity of the method to the more classical deprotonation. A few examples are given here [312,313]. 

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