Preparation of 3,5‐Dibromo‐2‐Pyrone From Coumalic Acid

Abstract The article discusses the synthesis of 3,5‐dibromo‐2‐pyrone was first reported by Pirkle and coworkers in 1969. It was prepared from 2‐pyrone by following either a three‐step sequence that involved two successive brominations and HBr elimination or a fourstep sequence that involved a bromination, HBr elimination, and photochemical bromination, followed by another HBr elimination. This complex and even cumbersome process would the best alternative yet as there is no other method available in the literature. In this reaction, coumalic acid underwent an electrophilic aromatic bromination at C3 and bromo‐decarboxylation at C5. 3,5‐Dibromo‐2‐pyrone is a potent neutral diene that can react with both electron‐poor and ‐rich dienophiles via either normal‐ or inverse‐demand Diels‐Alder cycloaddition reactions in good to excellent chemical yield and diastereoselectivity.