Synthesis Of Diarylacetylenes And 2-Methyl-3-Aminobenzofurans Using Calcium Carbide As An Alkyne Source

Calcium carbide is often used to prepare acetylene gas in industry,and then acetylene gas is used as an alkyne source to synthesize a variety of organic chemicals.However,acetylene gas is flammable and explosive,and its reaction device is complex and difficult to operate.Therefore,it is of great significance to explore an alkyne source which is rich sources,low price and easy operation to replace acetylene for the synthesis of a variety of organic compounds.Recently,there have been some reports on the direct synthesis of organic compounds using calcium carbide as a concise solid alkyne source.These reported methods have the characteristics of cheap and easy-to-obtain raw materials,simple operation,mild conditions and high yields,which make calcium carbide show bright prospects in organic synthesis.However,the research in this area is far from in-depth,so it is necessary to further expand the research work.Diarylacetylenes,as common intermediates in organic synthesis,have been widely used in organic synthesis,such as the synthesis of 1,2-diphenylethylene,benzil,and various cyclic compounds.Palladium and copper co-catalyzed Sonogashira coupling reactions of arylacetylenes and halogenated aromatic hydrocarbons are commonly used for their synthesis.However,these methods have some disadvantages,such as expensive raw materials,complex synthetic steps,the use of volatile organic solvents,and the requirement of high temperature or gas protection environment.Therefore,it is necessary to explore a new,green and cheap method to synthesize diarylacetylenes.Benzofurans,as a kind of substances with physiological activities,widely exist in drug molecules and natural products.They have anti-tumor,anti-virus,antibacterial,anti-inflammatory and other functions.They are widely used as nerve,cardiovascular,cerebrovascular and respiratory drugs.They are a class of extremely important heterocyclic compounds.Although there have been many reports on the synthesis of benzofurans,there are few reports on the direct synthesis of 3-amino-benzofuran compounds in one step.The only reports use expensive catalysts,harsh reaction conditions,long reaction steps,and complex substrates.Therefore,it is still of great significance to search for a new,simple and cheap method to synthesize3-amino-benzofuran compounds.Based on the above background,the synthesis of diarylacetylenes and2-methyl-3-aminobenzofurans using calcium carbide as a concise solid alkyne source are investigated in this thesis.These protocols have advantages of the use of abundant and inexpensive raw materials,mild reaction conditions,non-toxic and nonvolatile solvents,simple work-up procedure,and high yield.This paper consists of the following three parts:Part 1:The research progress and current situation of the synthesis of alkenyl,alkynyl-bearing and heterocyclic compounds using calcium carbide as an alkyne source in recent ten years are reviewed.Part 2:The synthesis of 1,2-diarylacetylenes from the reactions of calcium carbide with aryldiazonium tetrafluoroborates were investigated.The method was carried out at room temperature in a deep eutectic solvent（choline chloride/urea=1/2）with tetrakis（triphenylphosphine）palladium and cuprous iodide as a co-catalyst and sodium iodide as an additive.The method has the advantages of mild conditions,high yield,cheap and easy-to-handle raw materials,and non-toxic,non-volatile,cheap,easy-to-preparation and recyclable solvent.Eighteen compounds were obtained by this method.All compounds were characterized by ¹H NMR,¹³C NMR and HRMS.Part 3:The one-pot three-component synthesis of 2-methyl-3-aminobenzofurans using calcium carbide as a concise solid alkyne source,salicylaldehyde and secondary amine as substrates were studied.The method was carried out in basic condition with copper salt as a catalyst and DMSO as solvent at 100 ^oC under N₂atmosphere.It is a new method for the direct synthesis of 2-methyl-3-aminobenzofurans.Twenty-four products were obtained by this method,and their structures were characterized by ¹H NMR,¹³C NMR and HRMS.