O-lithiothiophenol equivalents: Generation, reactions, and applications in synthesis of hindered thiolate ligands

Treatment of 2-(phenylthio)tetrahydropyran (11) with tert-butyllithium in THF-HMPA at-90 °C followed by chlorotrimethylsilane or chlorotriethylsilane and then mercuric chloride-hydrogen sulfide affords 2-(trimethylsilyl)benzenethiol (13) or 2-(triethylsilyl)benzenethiol (14), respectively. Compounds 13 and 14 can also be obtained directly from thiophenol by conversion of the latter to lithium 2-lithiobenzenethiolate (16) followed by quenching of a THF solution of 16 at-78 °C with an equivalent of the appropriate chlorosilane; by this same procedure, 4-tert-butylbenzenethiol can be converted into 4-tert-butyl-2-(trimethylsilypbenzenethiol (18) via lithium 4-tert-butyl-2-lithiobenzenethiolate (17) and 2-naphthalenethiol can be transformed into 3-(trimethylsilyl)-2-naphthalenethiol (31) via lithium 3-lithio-2-naphthalenethiolate (30). Reaction of 13 with n-butyllithium in hexane followed by chlorotrimethylsilane gives 2, 6-bis(trimethylsilyl)benzenethiol (15) together with products derived from lithiation of the silyl methyl groups. Treatment of a solution of 16 in THF with dichlorodimethylsilane, dichlorodiethylsilane, 1, 2-dichlorotetramethyldisilane, or 1, 2-bis(chlorodimethylsilyl)ethane affords bis(2-mercaptophenyl)dimethylsilane (23), bis(2-mercaptophenyl)diethylsilane (24), l, 2-bis(2-mercaptophenyl)tetramethyldisilane (25a), or 1, 2-bis[(2'-mercaptophenyl)dimethylsilyl]ethane (25b), respectively. Oxidation of 23 yields 11, 11-dimethyl-11H-dibenzo[c, f]-[1, 2, 5]dithiasilepin (26). Treatment of 17 with diethyldichlorosilane and dichlorodiphenylsilane affords bis(5-terf-butyl-2-mercaptophenyl)diethylsilane (27) and bis(5-tert-butyl-2-mercaptophenyl)diphenylsilane (28), respectively. The latter compound upon exposure to air gives 29, the diphenyl analogue of 26. Thiophenol can be transformed into 1, 2-benzenedithiol (32a) by way of 12; similarly 4-tert-butylbenzenethiol can be converted into 4-tert-butyl-1, 2-benzenedithiol (32b). Compound 32a can be further transformed into 1, 2, 3-benzenetrithiol (34) via a trilithio species 33. The ¹H and ¹³C NMR spectra of dilithio salts 16 and 17 were determined.