Synthesis Of N-Vinylarylcarbamides And Benzothiazolopyrimidines Using Calcium Carbide As An Alkyne Source

Calcium carbide is often used in industrial production to produce acetylene gas,which is then used for further chemical synthesis.However,the use of acetylene gas for synthesis requires high-pressure equipment and protection against the dangers caused by the flammable and explosive nature of acetylene gas.The application of acetylene is therefore still very limited.In recent years,many papers have reported the direct use of calcium carbide as a surrogate for acetylene in organic synthesis,and these reactions can be carried out under simple laboratory conditions,demonstrating that calcium carbide is a cheap,safe and green alternative to acetylene.However,calcium carbide has not been studied very intensively and therefore further development of calcium carbide reactions is still of great importance.N-Vinylbenzamide is a common intermediate in organic synthesis and is widely used in total synthesis,photochemical reactions and other fields.Many methods have been reported for the synthesis of N-vinylbenzamide,but these methods still have some drawbacks,such as the use of expensive transition metal catalysts and raw materials,low atomic economy,and long reaction steps.Therefore,it is still important to explore a novel,cheap and simple method to prepare N-vinylbenzamide.Thiazolo[3,2-a]pyrimidines play an important role in medicinal chemistry because of their wide range of biological activities,such as antitumour,anti-inflammatory,anti-proliferative,calcium antagonistic and anti-HIV effects.2-Phenyl-4H-benzo[4,5]thiazolo[3,2-a]pyrimidineanaloguesastypical representatives of thiazolo[3,2-a]pyrimidine analogues may also have important pharmacological activity.Unfortunately,there are few methods for the synthesis of2-phenyl-4H-benzo[4,5]thiazolo[3,2-a]pyrimidines,and only few existing report have to use expensive metal catalysts and raw materials,and harsh reaction conditions.So it is necessary to develop a green and efficient,simple and inexpensive method for the synthesis of 2-phenyl-4H-benzo[4,5]thiazolo[3,2-a]pyrimidines.This thesis investigates the direct use of calcium carbide as a solid alkyne source instead of acetylene gas for the efficient synthesis of N-vinylarylamides via N-vinylation of arylamides and the synthesis of 2-aryl-4H-benzo[4,5]thiazolo[3,2-a]pyrimidines via a three-component one-pot reaction with aromatic aldehydes and 2-aminobenzothiazoles.These methods have salient features of the use of inexpensive reaction raw materials,mild reaction conditions,simple workup procedures,and high reaction yields.This thesis is divided into the following three parts:Part I:The recent research progress in the synthesis of important organic compounds through coupling reactions,cyclization reactions and addition reactions direct using calcium carbide as a solid alkyne source is reviewed.Part II:A method for the selective synthesis of N-monosubstituted vinylarylamide using calcium carbide as a solid alkyne source and aromatic amides as starting materials was investigated.The method was completed in 1 h at 120 ^oC using KOH and ^tBu OK as bases under the conditions of DMSO as solvent and N₂atmosphere.The method has advantages of high selectivity（only monosubstituted products are produced）,good yield,and low cost of the reaction materials.Twenty examples were prepared using this method.The obtained compounds were characterized by ¹H NMR,and ¹³C NMR for the determination their structures.Part III:A method for the synthesis of 2-aryl-4H-benzo[4,5]thiazolo[3,2-a]pyrimidines by one-pot reaction of aromatic aldehydes and 2-aminobenzothiazoles using calcium carbide as a solid alkyne source was investigated.The method was carried out at 120 ^oC using ^tBu OK as a base,Cu Br as a mediator,DMF as solvent under N₂ protection.It is a novel method for the synthesis of 2-aryl-4H-benzo[4,5]thiazolo[3,2-a]pyrimidines with simple steps,inexpensive raw materials,easy workup procedure and high yields.The method can also be extended to the synthesis of similar benzoxazoles.Twenty-nine examples were synthesized using this method and all products were characterized by ¹H NMR,¹³C NMR and HRMS for the determination of their structures.