Table 1.

Optimization of the reaction conditions.^a

Entry	Lewis acid	Solvent	Yield (%)b
1	ZrCl4	CH2Cl2	25
2	ZrCl4	EtOH	NR
3	ZrCl4	DMF	NR
4	ZrCl4	THF	NR
5	ZrCl4	TFE	13
6	TiCl4	CH2Cl2	15
7	SnCl4	CH2Cl2	28
8	Sc(OTf)3	CH2Cl2	12
9	EtAlCl2	CH2Cl2	70
10c	EtAlCl2	CH2Cl2	29
11d	EtAlCl2	CH2Cl2	68
12e	EtAlCl2	CH2Cl2	25

^aReaction conditions: 1a (0.25 mmol), 2a (0.3 mmol), Lewis acid (0.5 mmol), solvent (2.5 mL), rt, 24 h. ^bYields of the isolated products after column chromatography. ^cLewis acid (0.25 mmol). ^dLewis acid (1 mmol). ^eThe reaction was quenched after 5 hours to isolate the pyrroloindolines 4a, see Supporting Information File 1. NR, no reaction.