CHELESELECTIVITY AND ANTICHELESELECTIVITY .4. REACTION-ACCELERATING NEIGHBORING-GROUP EFFECTS IN THE CROSS-COUPLING OF VINYLBROMIDES WITH ALKYL-TRANSITION METAL REAGENTS

The cross-coupling of vinylbromides with Me4FeLi2 or Me4MnLi2 is disti nct accelerated if the vinylbromide is provided with an hydroxy group in the alpha-, beta- or gamma-position to the bromine atom (compounds 2-4). This was elucidated by intermolecular competition experiments an d is very probably due to chelate formation as the first reaction step . Corresponding neighboring-group effects as seen in the reaction with 2-4 were observed by treating 2 with Bu4MnLi2, the alpha-methoxy viny lbromide (5) with Me4MnLi2, the secondary amino vinylbromide (6) with Me4FeLi2, the tertiary amino vinylbromide (7) with Me4FeLi2 or Me4MnLi 2, and the beta-cyano vinylbromide (8) with Me4FeLi2. These effects al low very chemoselective cross-coupling. The observed cross-coupling wi th vinylbromides are believed to occur by oxidative addition (intramol ecular due to preceding chelate formation) with subsequent reductive e limination.