Table 1. Optimization of Conditions^a.

entry	ratio	solvent	catalyst	yieldb (%)
1	1:1:1	MeOH	Sc(OTf)3	24
2	2:1:2	MeOH	Sc(OTf)3	74
3	2.2:1:2.2	MeOH	Sc(OTf)3	64
4	1.3:1:1.3	MeOH	Sc(OTf)3	34
5	2:1:2	TFE	Sc(OTf)3	45
6	2:1:2	water	Sc(OTf)3	11
7	2:1:2	MeCN	Sc(OTf)3	36
8	2:1:2	solvent free	Sc(OTf)3	21
9	2:1:2	PEG40	Sc(OTf)3	17
10	2:1:2	MeOH	PTSA	64
11	2:1:2	MeOH	perchloric acid	43
12	2:1:2	MeOH	acetic acid	48
13	2:1:2	MeOH	NH4Cl	51
14	2:1:2	MeOH	ZrCl4	63
15c	2:1:2	MeOH	Sc(OTf)3	40
16d	2:1:2	MeOH	Sc(OTf)3	54

^aReaction conditions: unless otherwise stated, all the reactions were performed with 1a (1 mmol), glyoxal dimethyl acetal (60% in H₂O, 0.5 mmol), 2a (1 mmol), and catalyst (20 mol %) in solvent (0.5 mL) at 100 °C under microwave radiation for 1 h. PTSA = 4-methylbenzenesulfonic acid; TFE = trifluoroethanol.

^bIsolated yield.

^cGlyoxal (40 wt % in H₂O) was used as dialdehyde source.

^dHeated at 80 °C for 12 h in sealed vial using aluminum heating blocks.