Synthesis of Oxadiazoles Thiadiazoles and Triazoles Derived from Benzobthiophene.

摘要

In this work 3-chloro-2-chlorocarbonylbenzo[b]thiophene (>1) was prepared from cinnamic acid and then converted into the acid hydrazide >2. The azomethines >3a-e were prepared from the corresponding aryl aldehydes and the acid hydrazide >2. Treatment of compound >2 with formic acid gave the N-formyl acid hydrazide >4, which upon refluxing with phosphorous pentoxide or phosphorous pentasulphide in xylene yielded the corresponding 2- (3-chloro-1-benzothien-2-yl)-1,3,4-oxadiazole (>5) and 2-(3-chloro-1-benzo-thien-2-yl)-1,3,4- thiadiazole (>6). Reaction of >1-thiosemicarbazide >7 with NaOH leads to ring closure giving 5- (3-chloro-1-benzothien-2- yl)-4H–triazole-3-thiol (>8) which is converted into a number of derivatives >9-12 Reaction of >2 with phenyl isothiocyanate and NaOH afforded 5-(3-chloro- 1-benzothien-2-yl)-4-(phenyl)-4H-1,2,4-triazole-3-thiol  (>14).