Studies On The Synthesis And Bioactivity Of 3-thiadiazolyl Dihydro Benzo [e] [1, 3] Oxazine

The heterocyclic compounds have already become the focus point of the discovery of new pesticides due to their wide range of biological activity in recent years. Benzoxazine is a kind of hexa-heterocyclic compound containing nitrogen and oxygen atoms, and their derivatives 3,4-dihydro-2H-1,3-benzoxazines always exhibit a broad biological activity, such as anticancer, antitumour, bactericidal and fungicidal. This class of compounds has a broad foreground in the field of drug research. This paper mainly studied the synthesis method of 3-thiadiazolyl-1,3-benzoxazines. 14 novel 3-thiadiazolyl-1,3-benzoxazines were prepared, and their structures were characterized by IR,1HNMR and 13CNMR, some of them were chareacterized by ESI-MS. It was also investigated the fungicidal activity of the intermediate products 36a~36m and the target compounds 33a~33i, 34b.A series of 2-amino-5-alkyl-1,3,4-thiadiazoles 31a~31i wew synthesized by reactions of N-aminothiourea and carboxylic acid. Then, 2-(subsitituted aminomethyl) phenol 36b~36m were prepared by"one-pot reaction"of 2-amino-5-alkyl-1,3,4-thiadiazoles 31a~31i with salicylaldehyde. The target compound 3-thiadiazolyl-3,4-dihydro-2H-1,3-benzoxazines 33a~33i, 34a~34e were prepared by reactions of 2-(subsitituted aminomethyl) phenols with methylene chloride or aromatic aldehydes in the presence of catalyst.In order to obtain the highest yields of compounds 33a~33i, we investigated the effects of phase transfer catalyst, the amout of potassium hydroxide, reaction temperature and the amount of methylene chloride on the yields, and obtained the optimized conditions: 15 mol% phase transfer catalyst (based on phenols), 350mol% KOH, 95℃, 240mol% CH2Cl2. At the same time, we investigated the effects of different catalyst and solvent on the yields of 2-aryl-3-thiadiazolyl-3,4-dihydro-2H-1,3 -benzoxazines 34a~34e.The fungicidal activity of novel 3-thiadiazolyl-1,3-benzoxazines and thiadiazolylaminomethyl phenols 36a~36m were assayed, and the results showed compounds 36a~36m exhibited good fungicidal activity against Alternaria alternata as shown by compounds 36g~36i,36k,36l (70%~75%, at concentration of 25mg/L). Secondly, compounds 36h,36l showed 51% and 50% activity, respectively, against Botrytis cinerea.3-thiadiazolyl-1,3-benzoxazines exhibited the good fungicidal activity against Sclerotonia sclerotiorum as shown by compounds 33a,33c (69%,76%). Secondly, compond 34b showed 70% activity against Alternaria alternata.