Regioselective Suzuki cross-coupling reactions at the 2-position of di- and tribrominated pyrroles

The 2,3,4-tribromopyrrole 4 and the 2,3-dibromopyrrole 10 were shown to undergo regioselective Suzuki cross-coupling reactions at the 2-position. After optimization best yields in the reaction with 4-tert-butylphenyl boronic acid (5a) were 68% and 86%. Other boronic acids 5 were employed in the reaction with pyrrole 4 and gave the monosubstitution products 6 in 33-52% yield. A subsequent cross-coupling at positions C-3 and C-4 could be achieved on 3,4-dibromopyrrole 6a (84% yield).