THE SURFACE NATURE OF GRIGNARD-REAGENT FORMATION

The reaction of exo-2-norbornyl bromide with Rieke magnesium in ether at -70-degrees-C in the presence of tert-butyl alcohol-O-d gave exclusively exo-2-deuterionorbornane whereas the epimer endo-2-norbornyl bromide yielded a 1:1 mixture of endo- and exo-2-deuterionorbornane. Reaction of the epimeric bromides with Rieke magnesium in the presence of tert-butyl alcohol and a 10-fold equivalent excess of the radical trap deuterated dicyclohexylphosphine resulted in only 8% deuterium incorporation in the products. Treatment of exo-5-bromo-2-norbornene under identical conditions (tert-butyl alcohol-O-d, -70-degrees-C) yielded a 65:35 mixture of exo-5-deuterio-2-norbornene and 3-deuterionortricyclene. In the presence of tert-butyl alcohol and a 10-fold excess of deuterated dicyclohexylphosphine the reaction of exo-5-norbornenyl bromide gave the same mixture of products but with only 8% deuterium incorporated. These results strongly support the surface nature of the Grignard formation reaction.