Chapter 5.2: Five-Membered Ring Systems: Pyrroles and Benzo Analogs

Abstract

This chapter describes the synthesis and chemistry of pyrroles, indoles, and fused ring systems. Pyrroles and especially indoles continue to draw a lot of attention from the scientific community because of their prevalence in natural products and wide range of biological and materials science applications. Pyrrole syntheses have been organized systematically into intramolecular and intermolecular approaches as well as by the location of the new bonds that describe the pyrrole ring forming step. The chapter also discusses different routes to pyrroles starting from nonpyrrole heterocycles. In addition to copper, palladium has also been used to catalyze N-substitution reactions of pyrroles. Kwong studied the palladium-catalyzed amination of aryl mesylates, finding pyrroles to be effective substrates. N-substitution of pyrroles has been accomplished by carbonylation. Quaranta demonstrated this through a base-catalyzed carbonylation of pyrrole using carbonic acid diesters. This provided a straightforward, ecofriendly alternative to the traditional synthetic methods based on hazardous phosgene or phosgene-derivatives in the preparation of N-carbonyl derivatives.