A Highly Regioselective Route To Construct 4-methylthio Pyridazines And Pyrazole Compounds

Pyridazine,also called 1,2-diazine,is a common six membered heterocyclic skeleton and is often encountered as a structural component of compounds possessing biological activities such as antibacterial,analgesic,antihypertensive and so on.Moreover,this heterocycle is also useful for the preparation of several other heterocycles and construction of some self-assembled supramolecular architectures.Consequently,synthesis of these compounds has attracted considerable interest.Nevertheless,routes for the synthesis of sulfur-containing pyridazines from readily available substrates are fairly few.As we all known,alkylthio-containing skeletons have received considerable attention since they are found as structural elements in many bioactive compounds as well as electronic,magnetic,and optical materials.In addition,they are also versatile intermediates for further transformations,such as substitution,addition-elimination,transition-metal-catalyzed cross-coupling reaction,and electrophilic cyclization.Therefore,the synthesis and properties of alkylthio-substituted pyridazines is of great significance.On the basis of this concept,in this dissertation,we have first summarized various methods for the synthesis of pyridazines and the applications of sulfanyl groups in organic synthesis.Then we discussed a highly regioselective route to construct 4-methylthio pyridazines.At last,we further investigated the reaction conditions and regioselectively synthesis of pyrazoles.The main content is as follows:In chapter 1,we mainly summarized the methods for the synthesis of pyridazines and applications of sulfanyl groups in organic synthesis.In chapter 2,as a continuation of our previous work,using 2-methylthio-substituted 2-butene-1,4-dione as a substrate,we report a novel and regioselective route for the preparation of 4-methylthio substituted pyridazines.In chapter 3,we further investigated the reaction conditions and found that when we increased temperature and added a little acetic acid,pyrazole products can be obtained regioselectively.The structure of the compound ?-20h was further confirmed by X-ray single crystal diffraction.