Table 1.

Optimization reaction conditions for the one-pot three-component synthesis of 4a.

Entry	Catalyst (mol%)	Temperature conditions	Time (h or min)	Yield (%)
1	Catalyst-free	Room temperature	48 h	30
2	Catalyst-free	50 ˚C	24 h	56
3	Catalyst-free	Reflux	24 h	43
4	DBN (2 mol%)	50 ˚C	1 h	71
5	DBU (2 mol%)	50 ˚C	1 h	75
6	DABCO (2 mol%)	50 ˚C	1 h	80
7	ZrOCl2•8H2O (2 mol%)	50 ˚C	45 min	90
8	ZrOCl2•8H2O (1 mol%)	50 ˚C	70 min	81
9	ZrOCl2•8H2O (10 mol%)	50 ˚C	45 min	82