Synthesis of Heterocyclic Carbamates with Potential Activity in Plant Protection

Aryl- and heteroaryl carbamates (e.g. Carbaryl and Pirimicarb) are known as plant protection agents. Because many pests develop resistances, new carbamate structures are of interest in plant protection research. Our synthetic approach started with the preparation of heterocyclic enoles such as pyrones 3, quinolones 6, and coumarins, quinolines, and pyridones of the general structure 12. They were obtained from 1,3-dinucleophiles such as anilines 1 and 10, phenols 10, and azomethines 10 by cyclocondensation with malonates. The pyrones 3 reacts with dialkylcarbamoylchlorides 4 in the presence of a base to carbamates 5. Degradation of 3 gave 4-hydroxyquinolones 6 which reacted with 4 to carbamates 9. Methylisocyanate 7 led to carbamates 8. Anilines 10 (X = NH, R3-R3 = -CH=CH-CH=CH-) cyclize with 2-substituted malonates 11 to quinolones 12. Similarly, phenols 10 (X = O, R3-R3 = -CH=CH-CH=CH-) react to coumarins 12. Azomethins 10 (X = N-alkyl, N-aryl, R4 either alkyl, aryl or 6- or 7-membered rings) give with reactive malonates pyridones, tetrahydroquinolines or cycloheptapyridones 12. Monocyclic pyridones 12 were also accessible from dehydracetic acid, followed by oxygen exchange with amines. The reaction of dialkylcarbamoylchlorides 4 with enols 12 in the presence of bases formed carbamates 13. With methylisocyanate 7, carbamates 14 were obtained. The evaluation of the biological activity shows, that 2 representatives from structures 6 and 12 exhibit strong plant protection properties.