Synthesis of functionalized long-chain thiols and thiophenols for the formation of self-assembled monolayers on gold

The terminally 2-thienyl- and phenyl-substituted eicosane derivatives 4 and 5 were prepared by reacting 1-[(20-bromoeicosyl)oxy]-4-methoxybenzene (3) with 2-lithiothiophene and lithium diphenylcuprate, respectively. Reaction of 4 and 5 with BBr3 leads to the corresponding bromides 6, 7 which afforde d the aryl-substituted eicosanethiols 8 and 9 by nucleophilic substitution with thiourea. 4-Eicosylthiophenol (13) was prepared from eicosylbenzene (1 1) by chlorosulfonation and subsequent reduction of the sulfonyl chloride. Synthesis of the thiol 22 with phenylenedioxy groups incorporated in the al kyl chain involves formation of 19 from allyloxy(bromobutoxy)benzene (18) a nd (4-(2-thienyl)butoxy)phenol (17). Hydroboration of 19 yields the corresp onding alcohol 20, which under Mitsunobu conditions and subsequent reductio n with LiAlH4 can be transformed to 22.