Optimization of the reaction conditions^a.

Entry	Catalyst (mg)	Solvent	Time (h)	Yieldb (%)
1	Fe3O4@pectin (40)	H2O	5	58
2	Fe3O4@starch–SO3H (40)	H2O	3	65
3	Fe3O4@cellulose–SO3H (40)	H2O	2	82
4	Fe3O4@chitosan–SO3H (40)	H2O	2	89
5	Fe3O4@chitosan–SO3H (50)	H2O	2	89
6	Fe3O4@chitosan–SO3H (30)	H2O	3	75
7	Fe3O4@chitosan–SO3H (40)	EtOH	2	88
8	Fe3O4@chitosan–SO3H (40)	Solvent-free	2	30
9	Fe3O4@chitosan–SO3H (40)	THF	2	63
10	Fe3O4@chitosan–SO3H (40)	CH2Cl2	2	59

^aReaction conditions: aldehyde (1 mmol), hydroxylamine hydrochloride (1.5 mmol), β-keto ester (1.5 mmol), room temperature, solvent (10 mL).

^bIsolated yields.