Metal-Free Synthesis of 1,2,4-Triazines via a Coupled Domino Process in One-Pot

Background: 1,2,4-Triazine is a prominent structural core system present in numerous natural and synthetic biologically active compounds. The existing synthetic methodologies have mostly focused on 3,6- disubstituted-1,2,4-triazines and 3,5,6-trisubstituted-1,2,4-triazines. However, until now only a few methods have been developed for making 3,5-disubstituted-1,2,4-triazines. Objective: The primary objective of the study was to find an efficient and simple way to construct 3,5- disubstituted-1,2,4-triazines. Method: The arylethene (0.24 mmol), I2 (0.22 mmol), IBX(0.24mmol.) and DMSO (2 mL) were added to a round-bottomed flask equipped with a magnetic stirring bar. The reaction mixture was agitated at 110°C under air for 3h, then amidrazone (0.2 mmol) was added to the mixture and the reaction continued at 110°C for another 1.5h. Afterwards, water (20mL) was added and the reaction mixture was extracted with ethyl acetate (3 × 50mL). The organic phases was combined and concentrated under reduced pressure to distill ethyl acetate. The residue was further purified by column chromatography on a silica gel column with petroleum / ethyl acetate (5:1) as eluent to obtain the desired products. Results: We developed an operationally simple way of regioselectively synthesizing 3,5-disubstituted-1,2,4- triazines by a coupled domino strategy with terminal aryl alkenes and amidrazones in one-pot. The overall process involves three different reactions: iodination, Kornblum oxidation and condensation. Conclusion: The strategies exhibit high performance with moderate to high yields, using simple and readily available terminal aryl alkenes and amidrazones, representing a powerful tool for the formation of potentially biologically active derivatives.