Table 1. Optimization of the Synthesis of 2-Methyl-1,8-naphthyridine^ab (10).

entry	cat. (mol %)	solvent	temp. (°C)	time (h)	yield (%)
1			50	10	NR
2		H2O	50	12	NR
3		acetone	50	10	NR
4	ChOH(1)	acetone	50	24	52
5	ChOH(1)	H2O	50	6	99
6	ChOH (1)	H2O	rt	22	90
7	ChOH (0.5)	H2O	50	12	95
8	ChOH (0.5)	H2O	rt	24	57
9	NaOH	H2O	50	6	88
10	KOH	H2O	50	6	84
11	Et3N	H2O	50	6	NR
12	Et3N·(CH2OH)2c	H2O	50	6	NR

^aReaction condition: 2-aminonicotinaldehyde, 8 (0.5 mmol), and acetone, 9 (0.5 mmol) were stirred with ChOH (1 mol %) in H₂O (1 mL).

^bIsolated yield, rt: room temperature NR: no reaction,.

^c1:1 mixture.