Aromatic heterocycles, particularly furans and pyrroles, are structural motifs found in a vast number of biologically active natural and artificial compounds [1][2][3]. Other examples of practical applications of furans and pyrroles include dyes, polymers, and electronic materials [4]. Moreover, these heterocycles are employed as important intermediates in organic synthesis [5][6][7][8][9]. The successful application of furans and pyrroles in these and many other ways and their significance in applied and fundamental areas have placed them at the forefront of contemporary organic chemistry. A variety of methodologies and different protocols for their synthesis have been reported [1-3, 10-23] and become well established throughout decades. Among the variety of novel approaches for the synthesis of furans and pyrroles, transition metal-catalyzed transformations are arguably the most attractive methodologies . Several excellent reviews on the transition metal-catalyzed synthesis of monocyclic five-membered heterocycles have been published in the literature. Many of them were categorized by either the metal or the type of transformation. This chapter covers transition metal-catalyzed syntheses of furans and pyrroles. The main organization of this chapter is based on a heterocycle, wherein syntheses of a particular core are structured by the type of transformation and substrates engaged. Herein, we have tried to discuss equally the synthetic applicability of a method and mechanistic aspects and concepts implicated in the described transformations. A discussion of the mechanisms is given when needed to provide an idea about possible reaction pathways and the nature of the elementary processes involved in the catalytic transformation. It should be noted that the most essential and general catalytic reactions, as well as recent and conceptionally interesting transformations, are discussed in more detail in this chapter. Syntheses of furans and pyrroles via functionalization of the preexisting heterocyclic cores [37,[52][53][54][55][56][57][58][59][60] are not covered and, therefore, only reactions in which assembly of a heterocyclic ring occurs are described. In addition, the Pd-catalyzed synthesis of heterocycles is not covered herein, as this topic is covered in Chapter 6.
