The acidifying effects of chlorine and bromine: Little difference

Article abstract of DOI:10.1016/S0040-4039(97)00131-7

Lithium diisopropylamide deprotonates ortho- and para-bromochlorobenzene randomly at the two halogen adjacent positions. Obviously for steric reasons, the bulkier base lithium 2,2,6,6-tetramethylpiperidide favors the attack in the vicinity of the chlorine rather than the bromine atom to the extent of 2:1. At -75°C, both 2-bromo-3-chlorophenyllithium and 3-bromo-2-chlorophenyllithium isomerize to give 2-bromo-6-chlorophenyllithium. The latter species can be directly generated from 1-bromo-3-chlorobenzene.