Synthesis of Brominated 2-pyrones as Chameleon dienes via Hunsdicker Reaction of 2-pyrone Carboxylic Acids

Abstract

Due to its aromaticity, 2-pyrone does not undergo Diels-Alder [4+2] Cycloadditions as easily as other cyclic diene. 2-pyrones with electron perturbing substituents are often thermally stable and show higher reactivities. Various substituted 2-pyrones were prepared and used as key synthons, taking advantage of their excellent sterochemical control in the cycloaddition step, for the synthesis of many natural and unnatural compounds including taxol and a series of vitamin D3 analogs. Brominated 2-pyrones have an additional interesting feature that they can react with both electron rich and deficient dienophiles. Their versatility and usefulness as chameleon dienes are, howere, somewhat overshadowed by their poor availability. We report more affordable and convient synthetic methode of various bromo-2-pyrone in one step from readily available 2-pyrone carboxylic acids through bromo-decarboxylation, commonly known as Hundsdiecker reaction.