Optimization studies^a.

Entry	Catalyst	Solvent	Temp. (°C)	8 yield (%)
1	10	THF	80	67
2	11	THF	80	53
3	FeCl3	DCE	rt	0
4	FeCl3	DCE	80	0
5	TFA	THF	80	0b
6	10	i-PrOH	80	31
7	10	CH3CN	80	28
8	10	EtOAc	80	26
9	10	Toluene	80	24
10	10	THF	90	87
11	10	THF	100	96c

^aConditions: substrate 8 (0.2 mmol) and 5 mol% catalyst in 0.4 mL of solvent (0.5 M) in a 5 mL sealed tube were heated to the temperature indicated for 15 h. Yields were determined by ¹H NMR using CH₂Br₂ as an internal standard.

^b2 equiv. of TFA was used.

^c85% isolated yield.