Benzenethiol, toluene-4-thio1, and 3,5-dimethylbenzenethiol are doubly lithiated (on sulfur and on carbon) by n-butyllithium in tetramethylethylenediamine. C-Lithiation occurs ortho to the thiol group, and subsequent treatment with electrophiles provides a convenient approach to ortho-substituted arenethiol derivatives. The reactions with tetraisopropylthiuram disulfide provide direct access to the corresponding o-phenylene trithiocarbonates. Double lithiation of 4-methoxybenzenethiol results in C-lithiation adjacent to the methoxy group rather than the thiolate residue, indicating that methoxy is a more powerfully ortho-directing substituent in this type of metalation reaction. 3-Methoxybenzenethiol is lithiated between the methoxy and thiolate groups.
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Smith et al. (1989) studied this question.