Boric acid-catalyzed multi-component reaction
Also, in our exploration of the reusability of the catalyst in water after
completion of the reaction, the filtrate that remained as catalyst was subjected to
evaporation under reduced pressure, and the recovery solid catalyst was applied as
such for the consecutive runs in five series of the same model reaction under the
optimized conditions for up to five runs (1st use: 90 %; isolated yield; 2nd use:
87 % isolated yield; 3rd use: 82 % isolated yield; 4th use: 76 % isolated yield; 5th
use: 70 % isolated yield). Decreasing the yield is probably related to the slight
reduction in the catalytic activity of the catalyst or the decreasin the the amount of
catalyst recovery which is attributed to the handling.
Conclusion
In summary, the efficient and clean synthesis of 4-arylidene-3-methyl-isoxazol-
5(4H)-ones (4a–h and 4l–p), 4-arylidene-3-phenyl-isoxazol-5(4H)-ones (4q–u), as
well as 3-(chloromethyl)-4-arylidene-isoxazol-5(4H)-ones (4v–x) via a one-pot
three-component condensation of b-ketoesters (3a–c), aryl aldehydes, and hydrox-
ylamine hydrochloride in the presence of boric acid as the catalyst at room
temperature has been developed. The reaction exhibited such merits as mild
conditions, easy work-up, completion of reaction in shorter reaction times, reuse of
catalyst, safety, and use of water with its ecologically friendly point of view.
Acknowledgment The authors are grateful to the Research Council of Damghan University.
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