Table 1. Optimization of the Reaction Conditions^a.

entry	additive	time (h)	solvent	temperature (°C)	yield (%)b
1	TFA	5	PhMe	80	8
2	TFA	5	PhMe	100	65
3	TFA	5	PhMe	130	81
4	TFA	5	PhMe	150	76
5	PhCOOH	5	PhMe	130	83
6	AcOH	5	PhMe	130	89
7	TfOH	5	PhMe	130	90
8	CuCl2	5	PhMe	130	7
9	AuBr3	5	PhMe	130	68
10		5	PhMe	130	74
11	TfOH	5	DCE	130	88
12	TfOH	5	MeOH	130
13	TfOH	5	DMSO	130	3
14	TfOH	5	1,4-dioxane	130	trace
15	TfOH	5	DMF	130	trace
16	TfOH	5	MeCN	130	10
17	TfOH	12	PhMe	130	81
18	TfOH	5	PhMe	150	67

^aReaction condition: 1a (0.5 mmol), 2a (1 mmol), and additive (2 equiv) in solvent (2 mL) were stirred at a temperature under air for 5–12 h.

^bIsolated yield.