Optimization of the catalyst, synthesis condition, and solvent for the synthesis of 4H-pyran in the model reaction^a.

Entry	Solvent	Catalyst (mol%)	Temp (°C)	Time (min)	Con. yieldb	Yieldc (%)
1	EtOH	1	70	60	85	75
2	DMF	1	100	30	70	65
3	THF	1	60	60	40	25
4	Dioxane	1	100	60	90	75
5	CH3CN	1	100	60	60	45
6	Toluene	1	100	60	90	80
7	PEG-400	1	70	60	95	88
8	H2O	1	70	15	100	98
9	Neat	1	70	60	98	90
10	Neat	1	70	30	75	60
11	H2O	0.5	70	45	90	80
12	H2O	0.7	70	30	95	87
13	H2O	1	70	15	100	97
14	H2O	1.2	70	15	100	98
15	H2O	1	25	60	80	65
16	H2O	1	45	30	93	85
17	H2O	1	55	15	100	97
18	H2O	1	65	15	100	98
19	H2O	1	75	15	100	98

^aReaction conditions: aldehyde (1.0 mmol), malononitrile (1.0 mmol), ethyl acetoacetate (1.0 mmol), catalyst (1 mol%) and H₂O (2 mL), 55 °C.

^bConversion yield (%).

^cIsolated yield (%).