Dilithiation of Methyl Phenyl Sulfide and Subsequent Trimethylsilylation

16 Dilithiation of Methyl Phenyl Sulfide and Subsequent Trimethylsilylation 

As shown in Exp. 14, methyl phenyl sulfide can be successfully converted into LiCH2SPh with one mol equivalent of the BuLiTMEDA reagent. Very recently Cabiddu et al. [1] reported that the mono-lithium compound can be specifically lithiated at the ortho-carbon atom in the ring by prolonged treatment with a second equivalent or butyllithium. A useful synthetic application is the preparation of benzo[b]thiophenes by reaction of the dilithio compounds with acyl chlorides [2]. 

In the procedure described below, the formation of the dilithiated sulfide is demonstrated by the reaction with trimethylchlorosilane. The reaction time can be shortened considerably by carrying out the dimetallation at elevated temperatures and using hexane as the only solvent. 

A mixture of 0.05 mol (6.2 g) of methyl phenyl sulfide and 0.11 mol of TMEDA is placed in the flask. A solution of 0.06 mol (note 1) of butyllithium in 36 ml of hexane is added over a few s from a syringe. The temperature of the solution rises within a few min to ca. 40 °C and is kept at this level for an additional 15 min. An additional amount of 0.05 mol of BuLi in 32 ml of hexane is then added and the mixture is heated at 55 °C for 45 min. A rather thick suspension is formed. After cooling to 

If necessary in connection with subsequent functionalization reactions, the excess of BuLi can be made inactive by adding a sufficient amount of THF ( 50 ml) which reacts with BuLi-TMEDA at room temperature to give ethene and H2C=CHOLi. 

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