Table 1.

Optimization of the reaction condition^a

Entry	Catalyst	Loading	Solvent	T (°C)	1H-NMR yield
1	Re2O7	2%	DCE	100	30%
2	HReO4	4%	DCE	100	24%
3	MeReO3(MTO)	2%	DCE	100	NR
4	(CO)5ReBr	2%	DCE	100	NR
5	Re(CO)10	2%	DCE	100	NR
6	Fe(OTf)3	2%	DCE	100	Trace
7	CuCl2	2%	DCE	100	NR
8	AlCl3	2%	DCE	100	NR
9	FeCl3	2%	DCE	100	NR
10	V2O5	2%	DCE	100	NR
11	Re2O7	2%	CF3CH2OH	100	54%
12	Re2O7	2%	HFIP	100	86% (85%)b
13	Re2O7	1%	HFIP	100	70%
14	Re2O7	2%	HFIP	80	69%
15	Fe(OTf)3	2%	HFIP	100	67%

^aReactions were performed with 1a (1.0 equiv.), solvent (0.2 M), catalyst (1–5 mol%) at 100 °C for 12 hours. ^bisolated yield.