Formal [4+1] cyclization of (thio/imido)hydrazides and ethyl 3,3,3-trifluoropropanoate: unified synthesis of 1,3,4-oxadiazoles, 1,3,4-thiadiazoles and 1,2,4-triazoles

Here we report an efficient and practical one-step synthesis of a series of 1,3,4-oxadiazoles with ethyl ester decoration, which was accomplished by the formal [4+1] cyclization of hydrazides and commercially available ethyl 3,3,3-trifluoropropanoate. In contrast to previously reported synthetic processes, this method features operational simplicity, easy scalability and good substrate tolerability. Furthermore, the present synthetic method can be generalized to access 1,3,4-thiadiazoles and 1,2,4-triazoles.