A USEFUL METHOD FOR CONFIGURATIONAL ASSIGNMENT OF VINYL SULFIDES - STEREOCHEMICAL REASSESSMENT OF THE RADICAL-ADDITION OF BENZENETHIOL TO ALKYNES

A comparative analysis of the H-1 NMR spectra of (E)- and (Z)-phenyl a nd alkyl sulfides and their corresponding sulfones provides a useful m ethod for establishing their configuration. Although by employing this method we generally confirm our previous configurational assignments for benzenethiol/alkyne adducts, those for (E)- and (Z)-3-(phenylsulfa nyl)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 conclu ded that radical addition of benzenethiol to alkynes at 100 degrees C generally proceeds with trans-stereo selectivity. This conclusion is t he reverse of our earlier claim for the effect that benzenethiol adds to terminal alkynes and alkyl-phenylacetylenes in a trans-stereoselect ive mode, but in a cis-stereoselective mode to dialkylacetylenes beari ng (rather) bulky alkyl groups.