SYNTHESIS AND BIOLOGICAL-ACTIVITY OF 1,2,4-THIADIAZOLINES .2. SYNTHESIS AND HERBICIDAL ACTIVITY OF FUSED DELTA(2)-1,2,4-THIADIAZOLINES

-5,6-dihydro-3H-thiazolo[2,3-c][1,2,4]thiadiazoles (III) were synthesi zed by oxidative ring closure of 3-(N-arylthiocarbamoyl)-2-iminothiazo lidines. And this synthetic method was successfully applied to the syn thesis of other 3-arylimino-1,2,4-thiadiazolo-fused heterocyclic syste ms. In foliage treatment this series of compounds exhibited fast-actin g and light dependent herbicidal actions which are similar to those of diphenyl ethers and tetrahydrophthalimides. The potency of the herbic idal activity was found to depend on both the substituents on the benz ene ring and heterocyclic moieties. Substituent effect of the benzene ring on the herbicidal activity was similar to that of tetrahydrophtha limides. Acid-catalyzed hydrolysis, base-catalyzed hydrolysis and phot o-decomposition of III were also studied. Several products were isolat ed and their structures were determined. However any 1,2,4-triazole-3- thione derivative, which is known to exhibit herbicidal activity simil ar to that of tetrahydrophthalimides, was not isolated. Under such che mical conditions, the rearrangement of 3-arylimino-1,2,4-thiadiazolo-f used ring systems to form 2-aryl-3-thio-1,2,4-triazolofused ring syste ms seemed to be difficult.