Efficient Green Approach for the Synthesis of Spiro[indoline-3,4′-pyrazolo[3,4-b]quinoline]diones Using [NMP]H₂PO₄ and Solvatochromic and pH Studies

Abstract

A mild and efficient protocol for the synthesis of spiro[indoline-3,4′-pyrazolo[3,4-b]quinoline]diones via a one-pot, three-component condensation of isatins, 1,3-dicarbonyls, and 5-amino-1-phenyl-3-methylpyrazole using [NMP]H₂PO₄ as a catalyst in EtOH/H₂O is described. The catalyst could be recycled and reused four times without significant loss of activity. Spiro[indoline-3,4′-pyrazolo[3,4-b]quinoline]diones with stabilized zwitter ionic resonance structures showed feasible application as new fluorescent probes and pH indicators. These chemosensors have a good wavelength shift and showed excellent sensitivity in the range of pH from 11 to 13.

GRAPHICAL ABSTRACT

Keywords:

• 5-Amino pyrazole
• β-diketones
• ionic liquid
• isatin
• multicomponent reaction
• spirooxindoles

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