ALKYNYL PHENYL SELENIDES AS CONVENIENT PRECURSORS FOR THE SYNTHESIS OF STEREODEFINED TRISUBSTITUTED ALKENES

The addition of p-toluensulfonic acid to alkynyl phenyl selenides is r egio- and stereospecific and affords (Z)-alpha-(phenylseleno)vinyl p-t oluensulfonates in good yield. alpha-(Phenylseleno)vinyl halides are o btained from the reactions of these compounds with magnesium halides. The reactions of (Z)-alpha-(phenylseleno)vinyl p-toluensulfonates with cyanocuprates afford the corresponding trisubstituted alkenes in whic h the tosyl group has been selectively substituted by an aryl or an al kyl group with retention of configuration. Finally, the cross coupling reaction of these vinyl selenides with methylmagnesium bromide, in th e presence of a nickel catalyst, occurs with retention of configuratio n and affords the selenium free trisubstituted alkenes.