The effect of the amount of ionic liquid on the reaction.

Entrya	Ratio	Time (h)	Yieldb (%)
1	0.01	2	80
2	0.05	2	85
3	0.1	2	93
4	0.2	2	93
5	1.0	2	93
6	0.1	4	98
7c	0.1	7	87
8d	0.1	4	90

^aReaction conditions: xanthen-9-ol (0.5 mmol), indoles (0.5 mmol), 50 °C.

^bIsolated yields.

^cThe reaction under room temperature.

^dThe reaction at 40 °C.