Study On Dehalogenation Reaction Of α-halomethyl Ketone(Cl,Br) Compounds

α-halogenated methyl ketone compounds are one of the intermediates with a wide range of uses in organic synthesis,and have certain pharmaceutical activity.At present,there are many synthetic methods forα,α-dihalomethyl ketones andα-halomethyl ketones,but it is still an important subject to study their simple and green methods.Althoughα-halogenated methyl ketones are important intermediates in organic synthesis,the existence ofα-halogenated methyl ketones in nature is harmful to ecological environment.Therefore,it is of great significance to study the dehalogenation methods ofα-halomethyl ketones.Part Ⅰ:Research on the reduction ofα,α,α-tribromomethyl ketones andα-monobromomethyl ketones by HBr/H₂O.Usingα,α,α-tribromomethyl ketone as the substrate,the reaction conditions for the reduction ofα,α,α-tribromomethyl ketone with HBr/H₂O were optimized by changing the mass fraction and amount of hydrobromic acid,solvent and temperature.Theα-bromomethyl ketone compounds with different substiuent are prepared.Then debromination ofα-bromomethyl ketones was studied,and the optimal conditions were obtained as follows:tetrahydrofuran was used as solvent,the debromination ofα-bromomethyl ketones with different substituents were carried out in the presence of 0.2 equiv.5%hydrobromic acid at 180 ℃.The method has the advantages of simple operation,good selectivity and good substrate applicability.Part Ⅱ:The reduction ofα,α,α-tribromomethyl ketones by H₂O.Usingα,α,α-tribromomethyl ketone as the substrate,the effects of different solvents,the amount of water and temperature were investigated.The optimal conditions for the preparation ofα,α-dibromomethyl ketones were obtained as follows:17 kinds ofα,α-dibromomethyl ketones were prepared at 180 ℃ with 10 equiv.water as reducing agent and 1,4-dioxane as solvent.The total debromination ofα,α,α-tribromomethyl ketones were also realized by selecting the temperature and the amount of reducing agent.The method has the advantages that the reducing agent is green and easy to obtain,no metal catalyst exists,and different products can be obtained by adjusting the reaction conditions.Part Ⅲ:Study on the reduction ofα,α,α-trichloromethyl ketones with H₂O.On the basis of the work described in Chapter 2,the synthesis ofα,α-dichloromethyl ketones was studied by using water as reducing agent.In contrast to debromination,higher temperature is required for dechlorination.Therefore,α,α-dichloromethyl ketones with different substituents were synthesized successfully at 180 ℃ using1,4-dioxane as solvent and adding 10 equiv.water.Finally,according to the literature and experimental results,the reaction mechanism was discussed.