Five‐Membered Heterocycles: Imidacloprid and Thiacloprid

The discovery of the five-membered heterocycles such as imidacloprid and thiacloprid was a result of a search for improved activity by altering the structure of the originally published six-membered nithiazine. In 1991, imidacloprid was introduced to market as the first member of the chloronicotinyl insecticide family, the most successful, highly efficacious, and best-selling insecticide worldwide at that time, important for the control of invertebrate pests in numerous crops. In connection with the excellent biological performance of imidacloprid, the extensive research program led to the discovery and development of thiacloprid. The different functional groups as part of the pharmacophores ( N -nitroguanidine and N -cyanoamidine) in their molecules are responsible for the insect nicotinic acetylcholine receptor ( n AChR) interaction. Both imidacloprid and thiacloprid are of interest as ectoparasiticides in veterinary medicine. This chapter describes the chemistry of these five-membered heterocycles, their efficacy on target pests, their application rates, and their current resistance development .