THE ACIDIFYING EFFECTS OF CHLORINE AND BROMINE - LITTLE DIFFERENCE

Lithium diisopropylamide deprotonates ortho- and para-bromochlorobenze ne randomly at the two halogen adjacent positions. Obviously for steri c reasons, the bulkier base lithium 2,2,6,6-tetramethylpiperidide favo rs the attack in the vicinity of the chlorine rather than the bromine atom to the extent of 2 : 1. - At -75 degrees C, both 2-bromo-3-chloro phenyllithium and 3-bromo-2-chlorophenyllithium isomerize to give 2-br omo-6-chlorophenyllithium. The latter species can be directly generate d from 1-bromo-3-chlorobenzene. (C) 1997 Elsevier Science Ltd.