New Porphyrinoids through Palladium-Catalyzed Couplings

Abstract

Concise and versatile syntheses of oligopyrrolic derivatives are crucial for the preparation of macrocycles such as porphycenes, bronzaphyrins or cyclopyrroles. However, these precursors are usually obtained via long and tedious synthetic pathways. Besides, the key reactions of these procedures (i.e., Ullmann coupling, Stetter condensation) often hamper the preparation of functionalized macrocycles. As an alternative to these reactions, palladium-catalyzed couplings have emerged as promising synthetic methodologies. Recently, our group has developed a new family of 2,2´-bipyrroles 1 that possesses a remarkable chemical stability, ascribed to the presence of electron withdrawing groups. This stability allows the preparation of α-brominated 2,2´-bipyrrole derivatives. With these halogenated 2,2´-bipyrroles in hand and using palladium-catalyzed cross-coupling reactions, such as the Suzuki coupling, a new family of chemically stable and easy-to-functionalize quaterpyrroles have been synthesized (2). A similar strategy has been applied to halogenated pyrroles to yield terpyrroles and related analogues (3). In this presentation, the preparation of such oligomers and their use to obtain new expanded porphyrins will be discussed. Figure 1