Paal–Knorr synthesis: An old reaction, new perspectives

Paal–Knorr (P–K) synthesis is an old name reaction in organic chemistry that generates either furans, pyrroles, or thiophenes, starting from 1,4-dicarbonyl compounds in acidic media. It is one of the most significant methodologies for the preparation of these five membered aromatic heterocycles. P–K synthesis has found several applications in the total synthesis of natural products. In this chapter, we update our previous chapter published in Advances in Heterocyclic Chemistry in 2014. It covers the advances made in the applications of P–K reaction in the synthesis of pyrroles, furans and thiophenes from 2015 till date. It also underscores the applications of P–K reaction in the total synthesis of natural products.