Lactic acid-catalyzed Eco-friendly Cyclization Reaction for the Synthesis of 4𝐻-benzo[𝑏] pyrans and 3,4- dihydropyrano[𝑐] chromenes in EtOH/H2O as an Efficient Green Reaction Medium

An environmentally friendly, green, and highly efficient process for the synthesis of biologicallyand pharmacologically 4h-benzo[𝑏] pyrans and 3,4-dihydropyrano[𝑐]chromenes is developed bycondensing cyclic aromatic aldehydes, malononitrile, and dimedone or 4‐hydroxycoumarin in thepresence of lactic acid as an efficient and green catalyst. the corresponding products have beensynthesized in 50–97% yield in middle condition reaction which confirmed the excellent catalyticactivity of the lactic acid. furthermore, this methodology shows unique advantages, such asoperational simplicity, short reaction time, high yields, low cost, absence of any tedious workup orpurification and avoidance of hazardous or toxic reagents/catalysts/solvents.