The Study On The Synthesis Of2-aminobenzothiazoles And1,3-oxazolidin-2-ones

This dissertation consists of part I and part II. Part I involves the reseach on thesynthesis of2-aminobenzothiazoles and part II involves the investigation on the synthesis of1,3-oxazolidin-2-ones using carbon dioxide as feedstock.2-Aminobenzothiazoles are an important class of heterocycle whose diverse biologicalactivities make them privileged scaffolds in drug discovery. For example, marketed Riluzoleis a2-aminobenzothiazole compound employed in the treatment of amyotrophic lateralsclerosis; They have also been widely used to develop anti-diabetic, anti-microbial, anti-viral,anti-cancer, anti-parkinsonian agents and so on. Therefore,2-aminobenzothiazole derivativesplay an important role in medicinal chemistry. In part I, it is presented that various2-aminobenzothiazole were metal-freely prepared from cyclohexanones and thioureas in theacidic conditions catalyzed by iodine with oxygen as an oxidant. This transformation wasconducted in DMSO at75oC for24hours by adding30mol%iodine and5equivp-toluenesulfonic acid.2-substituted,4-substituted,3-substituted cyclohexanones andnon-substituted, mono-substituted, N, N-disubstituted thioureas all went through the process.It is worth noting that2-aminonaphtho[2,1-d]thiazoles and2-aminonaphtho[1,2-d]thiazolescan be prepared via this method in satisfactory yield, whose practical synthetic processes havenot been reported. This strategy also employs oxygen as a green oxidant and avoids transitionmetals.Carbon dioxide is the major greenhouse gas as well as the most abundant carbonresourse in the earth. Chemical fixation of carbon dioxide is of great importance from theviewpoint of the protection environment and carbon resourse utilization. In part II, it wasinvestigated that carbon dioxide was chemically fixated into1,3-oxazolidin-2-ones. Firstly,CuI/SnCl2Co-Catalyzed four-component assembly of carbon dioxide, alkynes, amines andketones to afford1,3-oxazolidin-2-ones. This conversion was carried out in DMSO at70oCfor12hours under CO2pressure of1.5MPa by adding30mol%CuI and20mol%SnCl2togive1,3-oxazolidin-2-ones in good yield. This reaction is an example that ketones, terminalalkynes and primary amines can go across a A3-type coupling, and linear or cyclic aliphaticketones are good substrates while aromatic ketones are not due to its steric hindrance. In the course of the above research, it was found that carbon dioxide, terminal alkynes and primaryaimines could also reaction in the absence of ketones to produce another1,3-oxazolidin-2-ones. The three-component cycloaddition reaction was performed under CO2pressure of2MPa at90oC for24hours under solvent-free conditions using10mol%CuI ascatalyst. Primary aliphatic amine with strong nucleophilicity and aryl-substituted terminalalkynes were good substrates.5-Alkylidene-1,3-oxazolidin-2-ones are commonly synthesisfrom carbon dioxide and costly propargyl amines while they can be prepared for moreavailable alkynes, ketones, amines and carbon dioxde via the protocols in part II of thisdissertation.