Thiazole and Isothiazole Ring–Containing Compounds in Crop Protection

Organic compounds containing five-membered aromatic heterocyclic rings play an important role in life science. Among them thiazole and isothiazole heterocycles are present in many pharmaceutical drugs and crop protection compounds and have sparked over past years an enormous interest on these scaffolds. In agrochemicals these moieties are found in 11 commercial products as well as in two development compounds. A thiazole moiety is present in seven currently marketed agrochemicals, namely the insecticides thiamethoxam and clothianidin, the fungicides thiabendazole, thifluzamide, ethaboxam, and oxathiapiprolin, and the nematicide fluensulfone, as well as in the development compound dicloromezotiaz. One compound, the fungicide isotianil, contains an isothiazole ring and three compounds a benzothiazole ring, namely the fungicide benthiavalicarb and the herbicides methabenzthiazuron and mefenacet. A benzisothiazole ring is not yet present in any commercial product, however, is found in the former nematicide development compound benclothiaz. Interestingly thiazole and isothiazole heterocycles are much less frequently found in agrochemicals than pyridine and pyrazole despite their bioisosteric relationship, which may indicate that these heterocycles have still not been explored to their full scope in crop protection lead discovery and optimization. Detailed information on the discovery, synthesis, and the structure–activity relationships of thiazole- and isothiazole-containing agrochemicals is provided in this review.