One‐Pot Three‐Component Domino Synthesis of Isoxazolo[5,4‐b]pyrano[2,3‐f]quinolines: An Efficient Fluorescent Turn‐off Chemosensor for Picric Acid

Abstract The synthesis of novel isoxazolo[5,4‐ b ]pyrano[2,3‐ f ]quinoline hybrids has been achieved through a one‐pot three‐component reaction of 3‐methyl‐7,8‐dihydroisoxazolo[5,4‐ b ]quinolin‐5(6 H )‐one, isatins or aromatic aldehydes and malononitrile in the presence of a base at ambient temperature. The reaction occurred through a domino Knoevenagel‐Michael type addition‐ O ‐cyclization sequence in a single transformation to afford the products in excellent yields. One of the isoxazolo[5,4‐ b ]pyrano[2,3‐ f ]quinoline was found to be highly sensitive towards picric acid with a lower limit of detection of 1.2 μM and quenching constant of 2.02×10 3 M −1