Study On The Environmentally Friendly Synthesis Of Benzothiazoles And Quinoxaline Derivatives

Of the more than 20 million chemical compounds currently registered, about one half contain heterocyclic systems. Heterocycles are important, not only because of their abundance, but above all because of their chemical, biological and technical significance. Heterocycles count among their number many natural products, such as vitamins, hormones, antibiotics, alkaloids, as well as Pharmaceuticals, herbicides, dyes, and other products of technical importance (corrosion inhibitors, antiaging drugs, sensitizers, stabilizing agents, etc.). The scope of application of heterocycles continuously expands. There has been tremendous interest in developing efficient methods for the synthesis of heterocylic compounds.At present, the green organic synthetic chemistry, which is developing environmentally friendly methods in organic synthesis, has attracted more and more attention. Poly(ethylene glycol) (PEG) has many applications, not only in chemistry but also in other diverse disciplines as well. PEG has become very popular in organic synthesis since they are nonvolatile, recyclable, stable to acid, base, and high temperature, and available in high quantities at low prices. Furthermore, their well-known low toxicity makes them greener versions of conventional halogenated solvents.At the same time,the search for the recyclable catalyst is still being actively pursued. Immobilization of Pd (II) catalysts on polymers can be recycled several times. This immobilized Pd (II) catalyst can be removed after reaction by simple filtration with the advantages of easy separation, recyclablity and easy purification of products; in addition, the micro-environment of polymer adjacent chain is differ from the micro-environment in the solution reaction, such difference will lead to a favorable response rate and the special effects.This dissertation is classified into three chapters:Chapter 1 The application of PEG in the Synthesis of Heterocycles.In this chapter we reviewed the development and application of PEG in the synthesis of heterocyclic compounds in recent years in detail.Chapter 2 An Efficient and Reusable Polymer-Supported Palladium- PEG-H2O Catalytic System for the Synthesis of Benzothiazoles.A novel and efficient method has been developed for the synthesis of benzothiazoles and benzoxalines via the cyclocondensation of 2-aminothiophenol and 2-aminophenol with aldehydes catalyzed by polystyrene-supported palladium in PEG-water under air. The polymeric catalyst can be reused more than 10 times. PEG and H2O are environmentally benign reagents which can avoid using hazardous and toxic organic solvents.Chapter 3 Synthesis of Quinoxaline Drivatives Catalyzed by PEG-400 and Extend to the Synthesis of BenzothiazolesPolyethylene glycol (PEG) was found to be an effective catalyst for the condensation of 1,2-diamines with 1,2-dicarbonyl compounds to afford the corresponding quinoxaline derivatives in excellent yields under mild reaction conditions.