Pyrrole as a Directing Group: Regioselective Pd(II)-Catalyzed Alkylation and Benzylation at the Benzene Core of 2‑Phenylpyrroles

Pyrrole has been employed for the first time as a directing group
in the Pd(II)-catalyzed ortho-functionalization of
C(sp2)–H bonds. A variety of substituted 2-phenylpyrroles
were successfully methylated, alkylated, or benzylated in the ortho-position of the benzene ring, yielding the respective
2-substituted pyrrol-2-yl benzenes (36 examples, 51–93% yield).
Neither additives nor additional ligands were required to perform
the reaction, which was routinely conducted with PdBr2 as
the catalyst and Li2CO3 as the base. Mechanistically,
there is evidence that precoordination of palladium to the pyrrole
enables the regioselective ortho-attack.