Regioselective Bipyrrole Coupling of Pyrroles and 3-Substituted Pyrroles Using Phenyliodine(III) Bis(trifluoroacetate)

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.