A useful method for configurational assignment of vinyl sulfides; stereochemical reassessment of the radical addition of benzenethiol to alkynes

A comparative analysis of the 1H NMR spectra of (E)- and (Z)-phenyl and alkyl sulfides and their corresponding sulfones provides a useful method for establishing their configuration. Although by employing this method we generally confirm our previous configurational assignments for benzene-thiol/alkyne adducts, those for (E)- and (Z)-3-(phenylsulfanyl)hex-3-ene and 4-(phenylsulfanyl)oct-4-ene, are shown to have been assigned incorrectly. In the light of the present results it is concluded that radical addition of benzenethiol to alkynes at 100 °C generally proceeds with trans-stereoselectivity. This conclusion is the reverse of our earlier claim for the effect that benzenethiol adds to terminal alkynes and alkylphenylacetylenes in a trans-stereoselective mode, but in a cis-stereoselective mode to dialkylacetylenes bearing (rather) bulky alkyl groups.