One-pot Synthesis of 2-Substituted 4H-Chromeno[3,4-d]oxazol-4-ones from 4-Hydroxy-3-nitrocoumarin and Acids in the Presence of Triphenylphosphine and Phosphorus Pentoxide under Microwave Irradiation

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Abstract
2-Substituted 4H-chromeno[3,4-d]oxazol-4-ones are prepared from 4-hydroxy-3-nitrocoumarin and acids by one-pot reaction in the presence of PPh3 and P2O5 under microwave irradiation or by one-pot two-step reactions in the presence of Pd/C and hydrogen and then P2O5 under microwave irradiation. The fused oxazolocoumarins were also synthesized from 3-amido-4-hydroxycoumarins and P2O5 under microwave irradiation. The 3-amido-4-hydroxycoumarins are obtained almost quantitatively from 4-hydroxy-3-nitrocoumarin, acids and PPh3 under microwave irradiation, or in the presence of Pd/C and H2 on heating. Preliminary biological tests indicate significant inhibition of soybean lipoxygenase and antilipid peroxidation for both oxazolocoumarins and o-hydroxyamidocoumarins.