Table 4. Selected optimization conditions for the synthesis of chromene derivatives^a.

Entry	Catalyst (mol%)	Solvent	Temp. (°C)	Timeb (min)	Yieldc (%)
1	1	MeOH	25	5	40
2	1	Water	25	5	25
3	1	ACN	25	5	90
4	1	EtOH	25	5	92
5	1	Ethanol–water	25	5	60
6	1	THF	25	5	45
7	1	CH2Cl2	25	5	30
8	1	MeOH	25	10	40
9	1	ACN	25	10	80
10	1	EtOH	25	10	92
11	1	Ethanol–water	25	10	45
12	1	THF	25	10	50
13	1	CH2Cl2	25	10	40
14	1	EtOH	50	30	92
15	0.5	EtOH	25	30	85
16	2	EtOH	25	30	80
17	—	EtOH	25	180	30
18	—	EtOH	50	240	30

^aReaction condition: benzaldehyde (1 mmol), malononitrile (1 mmol).

^bReaction progress monitored by TLC.

^cIsolated yield.