| Summary: | 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.
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