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Stable 5,5´-substituted 2,2´-bipyrroles: building blocks for macrocyclic and materials chemistry.

Research paper by Gonzalo G Anguera, Brice B Kauffmann, Jose Ignacio JI Borrell, Salvador S Borros, David D Sánchez-García

Indexed on: 27 May '17Published on: 27 May '17Published in: Journal of Organic Chemistry



Abstract

The preparation and characterization of a family of stable 2,2´-bipyrroles substituted at positions 5,5´with thienyl, phenyl, TMS-ethynyl, and vinyl groups is reported herein. The synthesis of these new bipyrroles comprises three steps: formation of the corresponding 5,5´-unsubstituted bipyrrole, bromination and Stille or Suzuki coupling. The best results in the coupling are obtained using the Stille reaction under microwave irradiation. The new compounds have been fully characterized by UV-vis absorption, fluorescence and IR spectroscopies and cyclic voltammetry. X-ray single-crystal analysis of four of the synthesized bipyrroles indicates a trans coplanar geometry of the pyrrole rings. Furthermore, the substituents at positions 5,5´ remain coplanar to the central rings. This particular geometry extends the π-conjugation of the systems, which is in agreement with a red-shifting observed for the λmax of the substituted molecules compared to the unsubstituted bipyrrole. All these new compounds display a moderate fluorescence. In contrast with unsubstituted bipyrroles, these bipyrroles are endowed with a high chemical and thermal stability and solubility in organic solvents.