Construction Of N-heterocyclic Skeletons Of Sulfur-containing And Selenium-containing From N-acylazo Compounds

l,3,4-Thiadiazole and 1,3,4-selenadiazole are important five-membered Nheterocyclic compounds containing sulfur or selenium.Among their derivatives,2amino/imino substituted 1,3,4-thiadiazoles and 1,3,4-selenadiazoles exhibit a wide range of biological and pharmacological activities.However,to date,these two types of compounds are mainly synthesized by the cyclization reactions of hydrazone or diazonium salt with various sulfur/selenium-containing reagents.Therefore,new strategies for the construction of 2-imino-1,3,4-thiadiazole and 2-imino-1,3,4selenadiazole skeletons are highly desirable and will benefit the fields of biology and medicinal chemistry.In this dissertation,firstly a P(NMe2)3-mediated deoxycyclization reactions of Nacylazo compounds with isothiocyanates was developed for the synthesis of 2-imino1,3,4-thiadiazoles.Among the thirty-two products synthesized,twenty-five ones are new compounds.Built on these results,such deoxycyclization reactions were further employed in the construction of selenium-containing N-heterocyclic frameworks.Twenty-five new 2-imino-1,3,4-selenadiazoles were synthesized via the PBu3mediated deoxycyclization reactions of N-acylazo compounds with isoselenocyanates in high yields.The structures of 1,3,4-thiadiazole 4a and 1,3,4-selenodiazole 8d were further confirmed by X-ray crystallography.The above synthetic approaches utilizes inexpensive and readily accessible hydrazides as starting materials.They could be oxidized by iodine into N-acylazo compounds,which could be directly used in the next-step organophosphine-mediated deoxycyclization reaction without further purification.These synthetic strategies not only can avoid the purification of the less stable N-acylazo intermediates,but also has the advantages such as simple operation,broad substrate scope,no use of transition metals and gram-scale synthesis.