C. Limon Catalyzed Heterocyclisation: Microwave Assisted Rapid One Step Synthesis of Substituted 2-aryl benzoxazoles

摘要

The use lemon juice extract as mild and highly efficient acid catalyst offers a convenient, nontoxic, inexpensive reaction medium for the synthesis of 2-aryl benzoxazoles under microwave irradiation condition were described. The procedure is simpler, economical, milder, and faster, including cleaner reactions, high yield of products which makes it a useful and attractive process and is also consistent with the green chemistry theme which affords excellent yields. We have used extract of Citrus limonium species of lemon as natural catalyst for synthesis. As lemon juice provides acidic condition pH 2-3 and percentage of citric acid 5-7% is more, hence it works as natural acid catalyst. The results indicate that lemon juice is the best catalyst for the heterocyclisation process. Adopting green technology, we have successfully applied natural acid catalyst i.e. citrus limon extract for synthesis of 2-aryl benzoxazoles (3a-i) by reaction of 2-amino phenol and substituted carboxylic acid under microwave irradiation. The products were obtained in excellent isolated yields (80-90%). The synthesized benzoxazole derivatives were characterized by IR, 1HNMR, 13CNMR and Mass spectral analysis and evaluated for antimicrobial activity against gram positive (S. aureus) and gram negative (E. coli) bacterial and fungal strain A. niger.