Table 1.

Optimization the dimerization condition of 3-oxo-2-arylhydrazonopropanals 1a with ammonium acetate ^a.

Run	Base-Catalyst (mol%)	Solvent	Conv. Heating		Sonication		MW Irradiation
			Yield b %	Time (h)	Yield b %	Time (min)	Yield b %	Time (min)
1	No catalyst	EtOH	trace	15	trace	120	trace	30
2	Et3N (15)	EtOH	70	4	82	60	87	5
3	Et3N (25)	EtOH	78 c	3	89 d	50	94	3
4	Et3N (30)	EtOH	71	3	85	60	90	4
5	Et3N (25) e	EtOH	66 e	3	73 e	50	80e	3
6	Et3N (25) f	EtOH	60 f	3	68 f	50	73f	3
7	Et3N (25)	MeOH	71	4	82	50	89	4
8	Et3N (25)	isopropanol	70	4	80	60	88	4
9	Et3N (25)	n-hexane	34	6	52	80	63	10
10	Et3N (25)	acetic acid	32	4	40	70	50	6
11	Et3N (25)	DMF	30	6	45	100	55	10
12	Et3N (25)	toluene	35	5	50	90	65	10
13	pyridine (25)	EtOH	20	4	28	60	35	5
14	DABCO (25)	EtOH	17	5	20	80	28	7
15	DBU (25)	EtOH	15	5	18	70	25	8
16	NaHCO3 (25)	EtOH	10	6	10	80	15	10
17	K2CO3 (25)	EtOH	10	5	12	90	15	10
18	NaOH (25)	EtOH	12	5	14	80	18	9

^a Reaction conditions: Arylhydrazonopropanal 1a (5 mmol), ammonium acetate (10 mmol) and base-catalyst (15~30 mol%) in solvent (7 mL) at reflux temperature for conventional heating 3~6 h, ultrasonic irradiation at 80 °C (110 W) for 50~100 min, or microwave irradiation at 80 °C (200 W) for 3~10 min. ^b isolated yield. ^c Yield was 20% after 50 min. ^d Yield was 35% after 15 min. ^e Compound 1a (5 mmol) and ammonium acetate (5 mmol) were used. ^f Compound 1a (10 mmol) and ammonium acetate (5 mmol) were used. Conv. = conventional, MW = microwave.