Screening of catalysts and co-catalysts^a.

Entry	Catalyst	Co-catalysts	Yield (%)
			3a	4a	5a
1	Pd/C	w/o	6	<1	4
2	Pd/C	TsOH	85	<1	<1
3	Pd/C	PhCOOH	7	<1	5
4	Pd/C	CF3COOH	13	<1	4
5	Pd/C	CH3SO3H	20	<1	<1
6	Pd/C	Ti(OiPr)4	8	<1	3
7	Pd/C	Al(OiPr)3	5	<1	6
8	Pd/C	ZnCl2	<1	<1	<1
9	Pd/C	B(C6F5)3	6	<1	<1
10	Pd/C	Sc(O3SCF3)3	1	<1	1
11	Pd/C	Na2CO3	2	<1	7
12	Pd/C	K2CO3	1	<1	69
13	Pd/TiO2	TsOH	54	<1	<1
14	Pd/Al2O3	TsOH	4	<1	<1
15	Pd/CeO2	TsOH	11	<1	1
16	Pd/LDH	TsOH	<1	<1	9
17	Ru/C	TsOH	3	<1	<1
18	Rh/C	TsOH	54	13	<1
19	Pt/C	TsOH	39	31	<1

^aReaction conditions: catalyst (metal: 2 mol%), additive (10 mol%), 1a (0.5 mmol), 2a (0.5 mmol), mesitylene (2 mL), Ar (1 atm), temperature 160 °C, and time 2 h. Yields were determined by GC and are relative to 1a.