A series of electron-rich bipyrroles were prepared by the regioselective, phenyliodine(III)
bis(trifluoroacetate) (PIFA) induced oxidative coupling of pyrroles in the presence
of bromotrimethylsilane. Using pyrrole and 3,4-disubstituted pyrroles gave exclusively
2,2′-linked bipyrroles without the formation of other bipyrrole regioisomers. The
3-alkyl- or 3-aryl-substituted pyrroles gave unsymmetrical H-T dimers in high yields
as the major isolable α-linked bipyrrole products over the symmetrical H-H dimers.
The nature of the N-substituent significantly influences the regioselectivity of the
reaction, thus regiocontrolled bipyrrole coupling of N-phenyl- and N-benzyl-substituted pyrroles gave 2,3′-bipyrroles.
bipyrrole - hypervalent iodine compound - bromotrimethylsilane - oxidative coupling
- Lewis acid - regioselectivity
