Table 1.

Optimization of the conditions for the reaction between 1a, 2a, and 3a.^a

entry	catalyst	solvent	yield (%)b
1	—	1,4-dioxane	0
2	Bi(OTf)3	1,4-dioxane	36
3	AlCl3	1,4-dioxane	80
4	FeCl3	1,4-dioxane	44
5	NiCl2	1,4-dioxane	21
6	PTSA	1,4-dioxane	73
7	HOAc	1,4-dioxane	trace
8	AlCl3	EtOH	31
9	AlCl3	MeCN	50
10	AlCl3	PhMe	27
11	AlCl3	DMSO	62
12c	AlCl3	1,4-dioxane	55
13d	AlCl3	1,4-dioxane	51
14e	AlCl3	1,4-dioxane	40
15f	AlCl3	1,4-dioxane	72

^a1a: 0.5 mmol, 2a: 0.6 mmol, 3a: 0.6 mmol, catalyst: 0.05 mmol, solvent: 1 mL, 80 °C, 6 h. ^bIsolated yield, calculated with respect to 1a. ^cAlCl₃: 0.025 mmol. ^d50 °C. ^e2 h. ^f10 mmol-scale reaction.