Microwave-Assisted Facile and Convenient Synthesis of Imidazolines

Irradiation time is 2.50 min."Isolated yield.11 min (Table 2).The conventional thermal reactions were also performed for this transformation in the absence of microwave energy.The experimental results show that the yields of the products are relatively lower under this condition and the reaction times are longer, specially in the cases of 1b, 1h and 1j.In order to show the general applicability of this method, the reaction of benzonirtile was performed on a 100 mmole scale.The result (95% yield, 2.5 min) was comparable to that obtained by the small scale experiment.In order to show the effect of sulfur, a mixture of benzo nitrile (1a) and ethylenediamine was irradiated in the absence of sulfur.Under this condition, the reaction did not proceed at all and benzonitrile remained intact in the reaction mixture.The exact mechanism of the reaction is not clear at this time.However, a plausible explanation is that sulfur reacts with nitrile to produce thioamide.Thioamide reacts with ethylenediamine, which upon elimination of hydrogen sulfide and ammonia, produces 2-imidazoline.Evolution of hydrogen sulfide is a certification of the above statement.In conclusion, a simple and efficient procedure for the synthesis of 2-imidazolines has been explored.Mild reaction conditions, absence of solvent, shorter reaction time, easy and quick isolation of the products and excellent yields are main advantages of this procedure which make this method an attractive and useful contribution to the present method ologies. Experimental SectionGeneral procedure for the preparation of 2-imidazolines under microwave irradiation: A mixture of nitrile (4 mmol), ethylenediamine (16 mmol) and sulfur (1 mmol) was irradiated with microwave (720 W) for 1.2-11 min.After completion of the reaction as indicated by TLC (eluent: EtOAc/MeOH, 4 : 1), the reaction mixture was cooled to room temperature, cold water was added and then extracted with chloroform.The organic layer was dried over anhy drous N2SO4 and evaporated.Recrystallization of the crude