Ultrasound Promoted Green and Facile One-Pot Multicomponent Synthesis of 3,4-dihydropyrano[c]chromene Derivatives

Table 1

Optimization of reaction conditions with different solvents and catalysts for the synthesis of 𝟒𝐚^𝑎.

Entry	Catalyst	Solvent	Mol (%)	Time (min)	Yield (%)^b
1	Trisodium citrate	H2O	30	10	57
2	NH4OAc	H2O	30	10	70
3	L-proline	H2O	30	10	30
4	Nafion-H	H2O	50 mg	10	40
5	Amberlyst	H2O	50 mg	10	30
6	Sodium acetate	H2O	30	10	92
7	Sodium acetate	PEG	30	10	50
8	Sodium acetate	DMSO	30	10	36
9	Sodium acetate	DMF	30	10	28
10	Sodium acetate	EtOH	30	10	70
11	Sodium acetate	H2O	30	180	30^c
12	—	H2O	—	30	35^d

^aThe reactions were carried out at room temperature using 4-hydroxycoumarin (1 mmol), benzaldehyde (1 mmol), malononitrile (1.2 mmol), and catalyst (30 mol%) in water (5 mL) under ultrasound conditions, ^bYields refer to the precipitated products, ^cabsence of ultrasound conditions, ^dOnly ultrasound, no catalyst.