Oxidation of Bis(tert-butylthio) Selenide at Low Temperatures: Search for a Bis(alkylthio) Selenoxide

Article abstract of DOI:10.1021/jo00011a015

Oxidation of bis(tert-butylthio) selenide, t-BuSSeSBu-t (1a), by peracetic acid at -40 deg C leads to a monooxidation product (1a-O) whose 1H (two singlets) and 13C NMR spectra (four resonances) show that the two tert-butyl groups in 1a-O are magnetically nonequivalent.It cannot therefore be the bis(alkylthio) selenoxide, t-BuSSe(O)SBu-t (3a), and is either t-BuS(O)SeSBu-t, 5a (oxidation of 1a at S rather than Se), or t-BuSSeOSBu-t, 4a (formed by rapid isomerization of initially formed 3a).The fact that δ 77Se for 1a-O is 289 ppm downfield from δ 77Se for 1a is inconsistent with structure 5a and indicates that 1a-O has structure 4a, t-BuSSeOSBu-t.Reaction of t-BuSH with 1a-O gives 1a plus t-BuSOH, in accord with what would be expected for nucleophilic attack of the thiol on the selenium of 4a.While oxidation of 1a by peracid is thought to result initially in 3a, this thioselenoxide apparently isomerizes to 4a so rapidly, even at -40 deg C, that 4a is the first oxidation product detectable by NMR.These results are of significance with regard to several steps in the previously proposed (ref 4) mechanism (Scheme 1) for the formation of bis(alkylthio) selenides from the reaction of thiols with selenite.