This chapter focuses on dehydroacetic acid, triacetic acid lactone, and related pyrones. Dehydroacetic acid is mainly used to produce clopidol, a coccidiostatic agent. Small quantities are used as a preservativ for fruits and vegetables as well as a stabilizer for plastics. Its sodium salt is also of interest for these applications. 4-Hydroxy-6-methyl-2-pyrone (triacetic acid lactone) is a natural product of polyketide origin. Its 3-acetyl derivative, 3-acetyl-4-hydroxyd-methyl-2-pyrone (dehydroacetic acid), has been isolated from natural sources and is industrially available by dimerization of diketene. Preparation of pyrones dealt with in the chapter can be achieved by modifying previously existing pyrones or by cyclizing open-chain compounds. Biogenetic formation of triacetic acid lactone has been considered a derailment from fatty acid biosynthesis promoted by the absence of the reductant NADPH. The pyrones react at their different ring positions. © 1992, Academic Press Inc.