A broad range of benzophenone hydrazone derivatives was prepared and tested against selected chewing insect pests, allowing the analysis of structure-activity relationships. Good activity was found only when the aromatic rings were substituted at the 4-positions with an halogen atom and a triflate or perhaloalkoxy group. In contrast, a number of substituents on the hydrazone part led to active compounds, the best results being achieved with acyl-type substituents. The excellent laboratory and greenhouse activity of the best representatives was confirmed in semi-field trials against Spodoptera littoralis.

The insecticidal lead 1,1-difluorododec-1-ene was optimised. This compound has attractive insecticidal activity against tobacco budworm (Heliothis virescens), banded cucumber beetle (Diabrotica balteata), pea aphid (Aphis cracciovora), brown planthopper (Nilaparvata lugens), and green rice leafhopper (Nephotettix cincticeps). Among different pharmacophore analogues, only 1,1-dichlorododec-1-ene and 1,1-difluoro-2-iodododec-1-ene showed weak insecticidal activity, whereas similar compounds such as 1-chloro-1-fluorododec-1-ene, 1-fluorododec-1-ene, and 1,1-difluoro-2-bromododec-1-ene were inactive. Only bridge analogues with even-numbered carbon chains were active, for example 1,1-difluorodec-1-ene and 1,1-difluorotetradec-1-ene. Odd-numbered analogues such as 1,1-difluoronon-1-ene, 1,1-difluoroundec-1-ene, 1,1-difluorotridec-1-ene, and 1,1-difluoro-pentadec-1-ene showed no activity. Modification of the tail group led to the analogues 12,12-difluorododec-11-enoic acid and its methyl ester, 12,12-difluorododec-11-en-1-ol, 1,1-difluoro-12-methoxydodec-1-ene, and 12,12-difluorododec-11-enylamine, all of which showed insecticidal activity. 12,12-difluorododec-11-enoic acid methyl ester, 12,12-difluorododec-11-enoic acid, and 12,12-difluorododec-11-en-1-ol were also active against spider mites (Tetranychus ssp). Thus, in a first optimisation cycle, broad activity against insect pests and mites was discovered. Two requirements, the gem-difluorovinyl pharmacophore and an even-numbered carbon chain, were found to be essential for activity. This latter requirement is in line with the proposed mode of action, which involves inhibition of the ? -oxidation of fatty acids in insect mitochondria. In a second optimisation cycle, it was found that 6,6-difluorohex-5-enoic acid and its derivatives, such as acids, amides, and hydrazides, possess even superior properties as insecticides and acaricides. This led to the discovery of 6,6-difluorohex-5-enoic acid 2-[4-(4-trifluoromethylbenzyloxy)-phenoxy]-ethyl ester (CGA 304'111). This compound showed excellent performance in field trials against a wide range of pests, as well as a more favourable toxicological profile than earlier derivatives. For a largescale synthesis of CGA 304'111, five different synthetic routes for 6,6-difluorohex-5-enoic acid were developed. The best route involved radical addition of CBrClF2 to pent-4-enoic acid. Removal of bromine by hydrogenation, elimination of chloride and hydrolysis of the ester concluded this most efficient sequence. Thus, a practical synthesis for CGA 304'111 was identified, which allowed the preparation of samples on a several 100 g scale.

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