Pyrans and Their Benzo Derivatives: Structure and Reactivity

Oxygen-containing six-membered heterocycles, constitute a large family of compounds widespread in both natural and synthetic compounds. These include 2H-pyrans, 4H-pyrans, pyrylium salts, pyran-2-ones, pyran-4-ones and their benzo analogs. The reduced pyrans and pyrones as well as their benzo derivatives are also covered. Several of these compounds exhibit interesting biological activity and thus, have drawn considerable attention from the chemical community. In particular, the structure, properties, reactivity and synthesis of these compounds have been extensively investigated. This article focuses on the most recent data on theoretical methods, experimental structural methods, thermodynamic aspects regarding this class of compounds. The latest developments on the reactivity of pyrans, benzopyrans and major derivatives, particularly in the last 10 years, is also covered. Indeed, incredible efforts have been dedicated to the discovery of novel methodologies to functionalize compounds from this class, ranging from photocatalysis to metal-catalyzed methods. The reactivity at ring atoms and substituents is highlighted.