Table 1.

Optimization of reaction conditions ^a.

Entry	Solvent	Temp (°C)	Yield b (%)
1	1,4-dioxane	80	33
2	THF	80	42
3	CH3CN	80	31
4	Toluene	80	17
5	Methanol	reflux	57
6	Ethanol	80	68
7	Ethanol/H2O	100	55
8	Ethanol	50	74
9 c	Ethanol	50	95

^a Unless indicated otherwise, the reaction was performed with 3a (0.5 mmol), 1a isatin (0.5 mmol), and L-proline (0.5 mmol) in different solvents (10.0 mL) and temperatures for 5 h. ^b Isolated yield based on isatin. ^c 10 h.