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

Table 2

Ultrasound promoted synthesis of 3,4-Dihyropyrano[c] chromenes 4a–4p using NaOAc as a catalyst^a.

Entry	Ar^b	Product	Time (min)	Yield (%)^c	Melting point (°C)/(lit.)
1			10	92	256–259/(258–260) [8]
2			8	85	264–266/(266–268) [20]
3			6	82	246–248/(245–247)[21]
4			5	86	255–257/(257–259) [10]
5			6	76	282–284/(280–282) [10]
6			5	94	256–258/(258–260) [8]
7			7	82	247–249/(249–251) [22]
8			5	90	262–264/(260–262) [20]
9			6	88	258–260/(260–262) [23]
10			8	76	251–253/(250–252) [21]
11			10	92	238–240/(232–234) [8]
12			10	90	226–228/(228–230) [21]
13			8	90	246–248/(247-248) [11]
14			7	85	258–260/(262–264) [10]
15			5	94	258–260/(255-256) [10]
16			10	91	259-260/(261-262) [24]
17			20	88	256–259/(258–260)^d

^aReactions were carried out at room temperature for 5–10 minutes using 4-hydroxycoumarin (1 mmol), aromatic aldehydes (1 mmol), malononitrile (1.2 mmol), and sodium acetate (30 mol%) in water (5 mL) under ultrasound conditions, ^bAr: aromatic group as shown in Scheme 1, ^cyields refer to the precipitated products, ^dScale-up experiment was conducted on 5 g batch for the synthesis of 4a.