A Novel "One-Pot" Method For The Preparation Of Pyrazoles And Isoxazoles

"One pot" for its convenient, simple, and not every post-processing,advantages, and quickly get organic workers favor. Detected in the samereaction vessel, the first step reaction, the next step by joining the reactants toignite the next reaction until the product was obtained.Also said that "one pot"to control the reaction process by adding the reactants. In this issue wepropose a new type of "one pot", it is essentially different from the traditional"one-pot". The new "one pot" is not only all the reactants are added to controlthe reaction process by controlling the reaction conditions, reaction conditionsinclude: temperature, pH value, solvent, and pressure. We hope that conditionsremain unchanged, the reaction system is only a first step reaction, when theconditions change, the next step reaction immediately.Through the new "one pot" synthesis of isoxazole,the same yield with thetraditional "one pot". Under alkaline conditions, imidoyl chlorides areconverted to nitrile oxides.3,5-disubstituted isoxazoles are obtained by Cu(I)-catalyzed1,3-dipolar cycloaddition reaction betwwen nitrile oxides andterminal alkyne. Throughout the experiment, all reactants are added to the container, completely after the reaction of synthesis imidoyl chlorides, the PHvalue by changing the reaction system to ignite the cycloaddition reaction. Wealso studied the influence of substituent, chloride reagent, and solvent on thereaction. When1,3-dipole with electron-donating groups it is advancedreaction, on the contrary with electron-drawing groups inhibits the reaction.Molar chloride reagent is1.5times that of the aldehyde, oxime able tocomplete conversion of imidoyl chlorides; if the amount of chlorine oxime, itis easy to let the side effects of chlorine substitution on the benzene ring withelectron-donating. If to select DMF/H₂O (1:1) as solvent, only the aromaticacetylene reaction, and other acetylene does not react; if t-BuOH/H₂O the (1:1)as solvent, all reactions are valid.Through the new "one pot" synthesis of pyrazole, the same yield with thetraditional "one pot". Under reaction temperature at50℃, benzaldehydetosylhydrazone are converted to phenyldiazomethane.3,5-disubstitutedpyrazole and3-substituted pyrazole are obtained by1,3-dipolar cycloadditionreaction betwwen phenyldiazomethane and terminal alkyne or1-vinylimidazole. Throughout the experiment, all reactants are added to the container,and completely after the reaction of synthesis benzaldehyde tosylhydrazone,we increased the temperature of the reaction system to ignite the cycloadditionreaction. We also studied the influence of substituent, reaction temperature,and solvent on the reaction. When1,3-dipolar bodies with electron-donating,it is advanced reaction, on the contrary with electron-drawing groups inhibit the reaction. The first reaction as long as the reaction temperature does notexceed the second step reaction initiation temperature, the reactiontemperature has little effect on the reaction; second step exceeds its triggertemperature, the reaction temperature on the reaction has little effect. Here isthe first step in the reaction temperature to20°C, the second step the reactiontemperature is50℃. Reaction solvent on the experiment, it is conducive withwater-miscible solvents on the reaction, DMF, methyl cyanide will be able tomeet the requirements.