Study On Ring Opening Reaction Of Epoxides Catalyzed By NiH

Transition metal catalysis is an important part of organic synthesis chemistry,especially the construction of carbon-carbon bonds and carbon-hetero bonds catalyzed by transition metals is a top priority,and is widely used in the synthesis of natural products and drug molecules.With the continuous development of transition metal catalysis,the reactions involving metal hydrogen are gradually becoming a new research hotspot.A literature survey shows that nickel-hydrogen（NiH）in metallic hydrogen is mainly used to catalyze the functionalization of unsaturated hydrocarbons and halogenated alkanes.In this paper,NiH-catalyzed ring-opening reaction of epoxy compounds was studied using nickel trifluoromethanesulfonate as the metal catalyst and silane as the hydrogen source.The results show that under different solvent conditions,different results can be obtained by NiH-catalyzed ring-opening of epoxy compounds.The specific research contents of this paper are as follows.Under the condition of tetrahydrofuran solvent,after screening and optimization of the reaction solvent,transition metal,silane,ligand and other conditions,the optimal reaction conditions under the condition of tetrahydrofuran solvent were obtained.Under these conditions,12 aromatic acetaldehyde products were synthesized with the highest yield of 93.8%.Therefore,we speculate the possible reaction mechanism.The oxygen atom of the epoxy compound is first coordinated with the complex LNi ^IIH formed by Ni（OTf）₂,PMHS and ligand,and the carbon-oxygen bond at theαposition is broken under the influence of THF solvent.Carbon radicals,followed by hydrogen radicals attackα-C radicals,followed by 1,2-hydrogen migration to obtain the target compound.The method has the characteristics of low cost,mild reaction conditions,simple operation and environmental friendliness.Under the condition of DMSO solvent,NiH-catalyzed epoxy ring-opening gave 12α-hydroxyketone compounds with the highest yield of 72.4%.Therefore,we speculate the possible reaction mechanism.The oxygen atom of the epoxy compound first coordinates with the complex Ni ^IIH formed by Ni（OTf）₂and PMHS,and then the negatively charged oxygen atom in DMSO attacksα-C to open the ring and The negative hydrogen was removed,and then the negative hydrogen attacked the H onα-C to remove the hydrogen,the oxygen-sulfur bond was broken to remove the dimethyl sulfide,and then the metal nickel was inserted into H₂,and finally NiⅡH was removed to obtain the target compound.The method has the characteristics of low cost,mild reaction conditions,simple operation,short reaction time and environmental friendliness.Under the condition of alcohol solvent,NiH-catalyzed ring-opening of epoxy compounds is a conventional Lewis acid ring-opening reaction,and 27β-alkoxy alcohol compounds were synthesized with a yield as high as 100.0%.Therefore,we made a simple speculation on the possible reaction mechanism.Ni（OTf）₂first coordinated with the oxygen atom of the epoxy compound,and then the oxygen atom of the alcohol solvent attacked theα-C ring to open the ring,and then further transformed to obtain the target compound.The method shows good compatibility for both epoxy compounds and alcohol solvents,and has the characteristics of low cost,mild reaction conditions,simple operation,short reaction time,and environmental friendliness.The above reactions were all characterized by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry,and the possible reaction mechanism was proposed through literature reports and experimental results.