4‐Hydroxyphenylpyruvate Dioxygenase ( HPPD ) Inhibitors: Heterocycles

This chapter describes the discovery of 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting heterocycles from outside the triketone class. It includes pyrazolones, the first class to be commercialized, and isoxazole procides of diketonitriles. The structure–activity relationships and the synthesis of commercial products from these chemotypes are discussed. New to this edition, the azole carboxamides are also described. This novel class of HPPD-inhibiting heterocycles is as-yet uncommercialized but shows great promise and examples have dominated the recent patent literature.