Table 1.

Synthesis of the Schiff bases 5a–l using NH₄Cl (10 mol%)

Entry	Producta	R1, R2	R3	Yieldb (%)
1	5a	(C6H5)2	2-OH	92
2	5b	(C6H5)2	4-OCH3	82
3	5c	(C6H5)2	4-Cl	78
4	5d	(C6H5)2	4-NO2	75
5	5e	(C2H5)2	2-OH	88
6	5f	(C2H5)2	4-OCH3	84
7	5g	(C2H5)2	4-Cl	80
8	5h	(C2H5)2	4-NO2	77
9	5i	1-Piperidinyl	2-OH	90
10	5j	1-Piperidinyl	4-OCH3	86
11	5k	1-Piperidinyl	4-Cl	84
12	5l	1-Piperidinyl	4-NO2	74

^aReaction conditions: spiro[indoline-3,4′-pyran]-3′-carbonitrile derivatives 3a–c (10 mmol), aromatic aldehydes 4a–d (10 mmol), and NH₄Cl (10 mol%) in 10 mL ethanol/reflux, 2 h

^bIsolated yields