Synthetic Strategies Toward 2H‐, 4H‐Pyrans, and Pyranones: Recent Advances

Abstract Pyrans are a class of six‐membered heterocyclic rings containing five carbon atoms and one oxygen atom. They are non‐aromatic in nature, bearing two double bonds in the ring. The double bond position distinguishes the two pyran isomers, namely, 2 H ‐pyran and 4 H ‐pyran. When a saturated sp 3 carbon is located next to an oxygen atom, it is known as 2 H ‐pyran, and when it is at the 4‐position with respect to oxygen is known as 4 H ‐pyran. In 1962, by the thermal breakdown of 2‐acetoxy‐3,4‐dihydro‐2 H ‐pyran, 4 H ‐pyrans were produced for the first time, and their characteristics were explored. Numerous synthetic methods of pyran have been disclosed over time owing to their broad applications in diverse fields, mainly in drug design, pharmaceuticals, and material science. In this review, we highlight the recent advancements toward substituted 4 H ‐pyran, 2 H ‐pyran, 4‐pyranone, and 2‐pyranones, focusing on reports published from 2019 to till date, which play important roles in both organic synthesis and diverse types of functional molecules.