Electrocatalytic Halogenation Of Alkynes And Pyridine Derivatives

Organic halides are not only important intermediates in organic reactions,but also important structural units for building complex molecules.Disadvantage compared to conventional synthetic methods of organic halide complex and environmental pollution,electrochemical method uses the reaction that occurs on the electrode to replace the use of oxidizing or reducing drugs,and become a new,simple and environmentally friendly synthesis method that is currently being explored.The electrochemical chlorination reaction of alkynes is to directly oxidize the electrode to generate chlorine free radicals.The oxidation potential is high,so the substrate range is narrow.The bromination reaction of pyridine derivatives usually requires toxic bromination reagents or the use of oxidizing chemicals and metal catalysts.The conditions required for the reaction to proceed are both dangerous and harsh.This paper studies the halogenation of alkynes and pyridine derivatives under the conditions of electrochemical synthesis.This dissertation uses the electrochemical organic synthesis method to carry out the experimental investigation,which mainly includes two parts:(1)Photoelectric synergy to catalyze the oxydichlorination reaction of alkynesA method of photoelectric synergistic catalysis for the synthesis of dichloroketone from alkynes was studied.Catalytically active species cerium hexachloride ions are generated from cheap magnesium chloride hexahydrate and cerium trichloride catalysts in a solvent.Under the conditions of LED light source excitation and constant current,cerium hexachloride ions are oxidized by electrodes and excited by light through the LMCT mechanism to generate chlorine free radicals,and then react with alkynes to produce products.The yield of 2,2-dichloroacetophenone was 75%.Expanded to two types of substrates of terminal alkynes and non-terminal alkynes,as well as natural product substrates,with medium to good yields.It is worth noting that the drug molecule ibuprofen derivatives can also be compatible with the reaction,and the product yield 43%,achieving the effect of drug modification.(2)Electrochemical bromination reaction of pyridine derivativesWithout the use of catalysts and oxidants,a simple and sustainable electrochemical bromination scheme has been developed.By introducing a positioning group,an inexpensive and safe bromine salt can be used as a bromine source to control the regioselectivity of pyridine derivatives at room temperature.Good to excellent yields more pyridinium bromide derivative obtained,and the reaction can be carried out easily gram scale.The yield of 2-amino-5-bromopyridine was 93%.A total of 23 substrates of aminopyridine compounds and pyridine derivatives were expanded,with a medium to good yield.The gram-level reaction was explored,and 1.18 g of2-amino-5-bromopyridine was obtained with a yield of 69%.Preliminary mechanism studies have been conducted through controlled experiments and cyclic voltammetry studies,which proved the formation of bromine free radicals.By installing and removing the positioning group,the meta bromination of pyridine is realized.