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<p>In this work, a novel and green synthesis of pentacyclic-fused pyrano[3,2-<i>b</i>:5,4-<i>b'</i>]diquinoline-8-carboxylic acids (<b>7a-q</b>) has been developed via the Pfitzinger reaction of 5-methyl-1H-pyrano[3,4-<i>b</i>]quinolin-4(3H)-one (<b>9</b>) with various isatins (<b>8a-q</b>). The reaction employs the basic ionic liquid [BMIm]OH (0.5 equiv.) as an eco-friendly homogeneous catalyst in aqueous medium under ultrasonic irradiation at room temperature for 4–6 h, affording the desired products in 74–88% yields. This synthetic protocol offers several notable advantages, including experimental simplicity, mild and environmentally benign conditions (water as solvent, ultrasonic activation), elimination of conventional strong bases, easy work-up (filtration and recrystallization), and avoidance of hazardous organic solvents. The greenness of the method is further supported by Eco-scale scores (44–66), which fall within the range typical for pharmaceutical industry standards. This work provides a sustainable and practical approach to structurally novel pentacyclic quinoline derivatives of potential medicinal interest.</p>

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A novel and green synthesis of pentacyclic-fused pyrano[3,2-b:5,4-b']diquinoline-8-carboxylic acids using Pfitzinger reaction

  • 期刊论文

  • 发表日期：

    2026年6月24日

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  • Xinyu Hou,
  • Zhiwei Li,
  • Wenyu Ma,
  • Yang Li,
  • Tianyu Liang

摘要

In this work, a novel and green synthesis of pentacyclic-fused pyrano[3,2-b:5,4-b']diquinoline-8-carboxylic acids (7a-q) has been developed via the Pfitzinger reaction of 5-methyl-1H-pyrano[3,4-b]quinolin-4(3H)-one (9) with various isatins (8a-q). The reaction employs the basic ionic liquid [BMIm]OH (0.5 equiv.) as an eco-friendly homogeneous catalyst in aqueous medium under ultrasonic irradiation at room temperature for 4–6 h, affording the desired products in 74–88% yields. This synthetic protocol offers several notable advantages, including experimental simplicity, mild and environmentally benign conditions (water as solvent, ultrasonic activation), elimination of conventional strong bases, easy work-up (filtration and recrystallization), and avoidance of hazardous organic solvents. The greenness of the method is further supported by Eco-scale scores (44–66), which fall within the range typical for pharmaceutical industry standards. This work provides a sustainable and practical approach to structurally novel pentacyclic quinoline derivatives of potential medicinal interest.