Rapid four-component synthesis of dihydropyrano[2,3-c]pyrazoles using nano-eggshell/Ti(IV) as a highly compatible natural based catalyst

Table 1 Preparation of 5 h in the presence of NEST under various conditions

Entry	Conditions	Time (min)	Yield^a (%)
Entry	Solvent/catalyst (g)/Temp. (°C)	Time (min)	Yield^a (%)
1	H₂O/NEST (0.06)/r.t	180	55
2	H₂O/NEST (0.06)/Reflux	120	58
3	EtOH/NEST (0.06)/r.t	60	75
4	EtOH/NEST (0.06)/Reflux	60	80
5	H₂O:EtOH (1:1)/NEST (0.06)/r.t	45	83
6	H₂O:EtOH (1:1)/NEST (0.06)/Reflux	30	85
7	–/NEST (0.06)/35	90	77
8	–/NEST (0.06)/60	150	70
9	–/–/r.t	30	25
10	–/NEST (0.02)/r.t	45	85
11	–/NEST (0.04)/r.t	20	90
12	–/NEST (0.06)/r.t	15	94
13	–/NEST (0.1)/r.t	20	89

Reaction was performed with ethyl acetoacetate (1 mmol), 4-chlorobenzaldehyde (1 mmol), malononitrile (1 mmol), and hydrazine hydrate (2 mmol)
^aIsolated yield

ISSN: 2661-801X