Synthesis and Biological Activities of Some Novel Triazolothiadiazines and Schiff Bases Derived from 1,2,4-Triazole

3-substituted-4-amino-5-mercapto-1,2,4-triazoles are versatile compounds for constructing various biologically active heterocycles. To find more 1,2,4-triazole derivatives that may possess significant biological activities, we synthesized a number of novel 3-(4-ethoxyphenyl)-6-aryl-1,2,4-triazolo[3,4-b][1,3,4]thiadiazines and 4-(arylmethylidene)amino-5-(4-ethoxyphenyl)-3-mercapto-4H-1,2,4-triazoles. All the title compounds were characterized by elemental analysis and NMR data, and the compound 5f was investigated with X-ray crystallography (CCDC No. 611639). The plant-growth regulating effects of those Schiff bases were examined, and they showed an inhibiting effect on the growth of wheat radicles and radish radicles.