Screening of different catalysts on the synthesis of 2-phenyl-8H-thieno[2,3-b]indole.

Entrya	Type of catalysts	Catalyst (mol%)	Yieldb (%)
1	Brønsted acids	H2SO4	72
2		HCl	70
3		H3PO4	67
4		CH3COOH	75
5		CF3COOH	80
6	Lewis acids	AlCl3	73
7		FeCl3	57
8		ZnCl2	80
9		SnCl4	65
10		CuCl2	42
11	Control experiment	Fe3O4	—
12		Fe3O4@SiO2	—
13		Fe3O4@SiO2@(CH2)3Cl	—
14		[Urea]4[ZnCl2]	82
15		Fe3O4@SiO2@(CH2)3–[Urea]4[ZnCl2]	87

^aReaction conditions: acetophenone (2.0 mmol), indole (1.0 mmol), sulfur (5.0 mmol) and catalysis (10 mol%) were heated in DMF (1.5 mL) at 140 °C for 12 h.

^bYield of 2-phenyl-8H-thieno[2,3-b]indole was isolated by column chromatography (dichloromethane/petroleum ether).