Table 3 Optimization of the NH₄VO₃ catalyzed model reaction for the synthesis of Hantzsch 1,4-DHPs.

Entry	Solvent	Time(min)	Amount of catalyst (mg)	Temperature (°C)	Yield^a (%)
1	Dimethyl sulfoxide	20	15	Reflux	75
2	Polyethylene glycol	45	15	Reflux	90
3	Dimethylformamide	20	15	Reflux	45
4	Tetrahydrofuran	45	15	Reflux	37
5	Acetonitrile	20	15	Reflux	85
6	Water	20	15	Reflux	55
7	Ethanol	20	15	Reflux	93
8	Ethanol	45	15	Reflux	93
9	Ethanol	45	15	r. t	65
10	Ethanol	20	18	Reflux	93
11	Ethanol	20	21	Reflux	93
12	Ethanol	20	23	Reflux	93
13	Ethanol	20	14	Reflux	85
14	Ethanol	45	13	Reflux	70
15	Ethanol	45	12	Reflux	58
16	Ethanol	45	–	Reflux	31

Reaction conditions: 4-chlorobenaldehyde (1.0 mmol), ethyl acetoacetate (2.0 mmol), ammonium acetate (2.0 mmol), solvent (3.0 mL). ^aIsolated yields.

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