Synthesis of Pyrazoles and Isoxazoles from Allenyl Ketones and A New Additional Reaction for Synthesis of b-Halo Ketones

• Main Authors: Shu-Huei Wang, 王淑惠
• Other Authors: 李世元
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/85930026189372885183

博士 === 淡江大學 === 化學學系博士班 === 93 === Part I: Pyrazole and Isoxazole are well-known as useful synthetic intermediates and important structural units which are widely observed in natural products and biological active molecules. Several methods for synthesis of isoxazoles have been developed and reported and the cyclocondensation reaction of b-diketone with hydroxylamine is one of the most common used method. The limitation of this method is the unsymmetrical b-dicarbonyl compounds can not be prepared regioselectively. The condensation reactions of oxime dianions with esters provide a regioselective accesses to generate b-keto oximes, which then undergo cyclodehydrations to afford isoxazoles. We wish to report a new synthetic method which improves and permits a variety of substituted pyrazoles and isoxazoles are easily prepared. Pyrazoles were synthesized from a reaction mixture of hydrazine dihydrochloride, sodium methylate and allenyl ketone in anhydrous N, N-dimethylformamide at room temperature. Isoxazoles were synthesized from a reaction mixture of hydroxylamine hydrochloride, cesium carbonate and allenyl ketone in anhydrous dimethyl sulfoxide at room temperature. Part II: b-Halo carbonyl compounds are potentially biologically active molecules and important synthetic intermediates in organic synthesis. Recently, our laboratory reported a simple and an effective method for synthesis of a,b-unsaturated ketone which is an useful synthetic precursor for preparation of a,b-unsaturated ketone. A reaction mixture of a,b-unsaturated ketone, boron trichloride and ethylene glycol in dichloromethane was stirred at 0oC and b-chloro ketone was produced in high yield. The b-bromo ketone was obtained as the major product when a reaction mixture of a,b-unsaturated ketone , boron tribromide and ethylene glycol in dichloromethane was stirred at 0oC after 0.5h.