Scheme 24.

Various arylglyoxals in the synthesis of [l]benzopyrano[4,3-b]pyrrol-4-ones 82, 83, and 85. Reagents and conditions: (a) i: AcOH, reflux, 40 min; ii: an appropriate alkyl p-toluenesulfonate (TsOR₂), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), toluene, reflux, 1.5 h, 14 outputs with 73%–89% yield; (b) R₁=Ph, 4-CH₃OC₆H₄, 4-CH₃C₆H₄, 4-FC₆H₄, 4-ClC₆H₄, 4-BrC₆H₄, 2-thienyl; dimedone, 2-hydroxy-1,4-naphtoquinone barbituric acid, 1,3 dimethyl barbituric acid, I₂, DMSO, stirring, 100 °C, 7 h, 15 outputs with 15%–80% yield.