Study On The Synthesis Of 2-Substituted Benzothiazoles Under Photo-and Electrochemical Conditions

Benzothiazoles are a type of important nitrogen-containing heterocyclic compounds having a wide range of biological activities.They can be used as pesticides,herbicides,plant growth regulators in agriculture.They can also be used as a unique and versatile drug molecular scaffold due to its strong and important pharmacological activity.It is noted that the introduction of substituents at the C-2position of benzothiazoles has the greatest impact on their activity.Therefore,many researchers have focused on the development of efficient and economical methods for synthesizing various 2-substituted benzothiazoles.In this thesis,new methods for green and efficient synthesis of 2-substituted benzothiazole derivatives under photo-and electrochemical conditions are investigated.This thesis consists of five chapters.Chapter 1 Progress in the Synthesis of 2-Substituted BenzothiazolesIn this chapter,various synthetic methods of 2-substituted benzothiazoles are reviewed in detail.Chapter 2 Two-component synthesis of 2-substituted benzothiazoles under electrochemical conditionsThe reaction of o-aminothiophenols and aldehydes is studied by using tetrabutylammonium tetrafluoroborate（TBABF₄）as an electrolyte under electrochemical conditions at room temperature.A series of 2-substituted benzothiazoles were obtained in the yield of 58%-98%in only 20 minutes.And o-aminophenol and o-phenylenediamine can be used to generate 2-arylbenzoxazole and 1-benzyl 2-arylbenzimidazole,which also has a good reaction yield.The method does not require the addition of transition metal catalysts and oxidants.It shows advantages of mild conditions,short reaction times and excellent product yields.It is a green and efficient new method for the synthesis of 2-substituted benzothiazoles.Chapter 3 One-Pot,Three-Component Synthesis of 2-Substituted Benzothiazoles under Electrochemical ConditionsA novel one-pot,three-component reaction of o-aminothiophenols,aldehydes and malononitrile is studied under electrochemical conditions.The reaction is conducted by using TBABF₄ as an electrolyte and Cu I as a catalyst at room temperature for 2-4 hours.2-Substituted benzothiazoles with 18 examples are obtained in moderate to excellent yields.Chapter 4 One-Pot,Three-Component Synthesis of 2-Substituted Benzothiazoles under photochemical conditionsA novel one-pot,three-component reaction of o-aminothiophenols,aldehydes and malononitrile is studied under visible light photochemical conditions.With Eosin Y as a visible light photosensitizer,the reaction is conducted under the irradiation of 36 W of Compact Fluorescent Lamps（CFL）at room temperature for5 hours.A range of target products are obtained in moderate to excellent yields.The method uses a cheap and easily available photocatalyst.It shows mild reaction conditions,excellent yield and simple operation.Chapter 5 Summary and OutlookThe above-mentioned methods for the synthesis of 2-substituted benzothiazoles under photo-and electrochemical conditions are summarized.Some problems are presented and discussed.In the later stage,the development for the synthetic method and applications of 2-substituted benzothiazoles is prospected.