The Applications Of Silica Dichlorophosphate And Silica Sulfate In Solvent-free Synthesis Of Heterocyclic Compounds

The typical organic synthesis has long been carried out in organic solvents because reactions in solvents proceed homogeneously and exchange energy smoothly. However, most of organic solvents are volatile, flammable, toxic and unrecoverable. Solvent-free reactions, avoiding the use of organic solvents, are clean, effective and economical reactions, in which the safety is largely increased, workup procedure is considerably simplified and the cost is greatly reduced. Therefore, solvent-free organic reactions have attracted many interests in chemical industry. Indeed, most of solvent-free organic reactions occur in solid state, the tightly and regularly arranged structures of solids make the reactions proceed more efficiently and selectively than solution ones. Furthermore, due to the simplicity in process and handing, solvent-free reactions can be accelerated by means of grinding, microwave irradiation and ultrasonic irradiation.Silica supported reagents and catalysts have advantages of comfort in handling, low toxicity, no corrosion, easy separation after completion of the reaction and reusability, which make it promising for both academic and industrial applications. In this thesis, we designed and synthesized four series of heterocyclic compounds using silica supported reagents and catalysts under solvent-free conditions and a series of novel 2-aryl-3-(N-substituted carbazolyl)-thiazolidin- 4-ones was also synthesized using solution method.The research results are summarized below:1. A series of symmetrical and unsymmetrical 2, 5-disubstituted 1, 3, 4-oxadiazoles were efficiently synthesized from the cyclodehydration of diacylhydrazines by using silica-supported dichlorophosphate as a recoverable cyclodehydrant in solvent-free medium under microwave irradiation. This protocol has advantages of no corrosion, no environmental pollution, accelerated rate, high yield and simple work-up procedure.2. A series of symmetrical and unsymmetrical 2, 5-disubstituted 1, 3, 4-oxadiazoles were efficiently synthesized from the cyclodehydration reactions of aromatic carboxylic acids and aroyl hydrazines in solvent-free medium under microwave condition by using silica dichlorophosphate as cyclodehydrant. This protocol has advantages of short reaction time, no corrosion, no environmental pollution and simple work-up procedure.3. Silica dichlorophosphate has been proved to be an efficient and reusable catalyst for the synthesis of acylals from structurally diverse aldehydes with acetic anhydride under solvent-free conditions at room temperature. This protocol has advantages of high yield, mild condition, short reaction time, no environmental pollution, and simple work-up procedure.4. Silica sulfate has been proved to be an efficient and reusable catalyst for the synthesis of 14-aryl/alkyl-14-H-dibenzo [a, j] xanthenes under solvent-free conditions. This protocol has advantages of short reaction time, high yield, simple work-up procedure, no environmental pollution.5. A series of novel 2-aryl-3-(N-substituted carbazolyl)-thiazolidin-4-ones were synthesized from the reactions of appropriate amine, aldehyde and mercapto acid by using dicyclohexylcarbodiimide (DCC) as a cyclizing agent in dry ether at room temperature. This protocol has advantages of mild condition, short reaction time and high yield.