The Synthesis Of Nitrogen-containing Five-membered Heterocycles Induced By Molecular Iodine

Nitrogen-containing five-membered heterocycles are a class of important compounds,which existed in a wide range of drugs,pesticides,dyes and photoelectric materials et al.Because of the highly biological activities these molecules present and thus have been widely used as antitumor,antibacterial,antioxidant etc.Among the numerous methods for the construction of heterocycles,organic transformations promoted by molecular iodine have attracted considerable attention in recent years because of its low toxicity,low cost compared with transition metal catalysts,its readily availability,and the utility for a large variety of reactions.In this article,the synthesis of poly-substituted 2,3-dihydropyrroles and pyrroles via tandem reaction induced by iodine and the formation of1,4-dicarbonyl compounds through molecular iodine promoted free radical reaction were reported.A series of 66 target compounds were designed and synthesized,among which 49 structures were new compounds.It could be described as the following three portions:1.I2-mediated tandem Miachael/cyclization sequence was developed for the synthesis of a series of 24 polysubstituted 2,3-dihydropyrroles from chalcones and?-enamines.We have developed a novel method for the construction of new2,3-dihydropyrroles,and have surveyed the reaction conditions,such as various of solvents,temperature,ratio of substrates,additives and so on.The results showed that the optimal parameters were as follows: a mixture of chalcones,1.2 equivalent?-enamines,1.2 equivalent iodine and 1 equivalent K2CO3 together with 3 mL CH2Cl2 under 80? and obtained corresponding products in 23-93% yields.All of these products were new compounds.Moreover,the reaction between chalcones and ?-enamines mediated by iodine under solvent-free high-speed vibration milling(HSVM)conditions have been surveyed.The reaction conditions have been optimized as well,and a total of 28 parallel 2,3-dihydropyrroles were synthesized in 53-85% yields under the optimal reaction conditions.2.A tandem Miachael/cyclization/elimination sequence was reported for the formation of a series of 19 polysubstituted pyrroles from nitroolefins and?-enamines induced by iodine under solvent-free HSVM conditions.The influences of the vibration frequency and the reaction time were investigated,then a series of pyrroles were obtained in 72-94% yields under the optimal conditions.This method provide a efficient and environmentally friendly route for the synthesis of polysubstituted pyrroles in a shorter period of time(20 min).3.A novel method for the synthesis of a series of 1,4-dicarbonyl compounds via iodine-promoted free radical reaction of the Michael addition product of chalcones and electron-withdrawing group substituted acetonitriles was reported.We have discussed and selected the reaction parameters,then concluded the optimal conditions were as follows: addition compounds,1 equivalent molecular iodine and 3 mL ethanol under 50 ?,a series of 19 products were obtained in51-92% yields.This method avoid using transition metal and toxic sovent in the synthesis of 1,4-dicarbonyl compounds thus less harmful to our environment.Moreover,a probable free radical mechanism was put forward.