Table 1. Optimization of Reaction Conditions^a.

entry	catalyst (mol %)	time (h)	temperature (°C)	1a:2a	yield (%)c
1b	[Cp*RhCl2]2 (5)/AgSbF6 (20)	24	110	1:2	20
2b	[Cp*RhCl2]2 (5)	24	110	1:2	0
3b	AgSbF6 (20)	24	110	1:2	29
4	FeCl3 (20)	24	rt	1:2	31
5	AlCl3 (20)	24	rt	1:2	0
6	BF3·Et2O (40)	24	rt	1:2	15
7	BF3·Et2O (20)	24	rt	1:2	22
8	BF3·Et2O (10)	24	rt	1:2	32
9	BF3·Et2O (5)	24	rt	1:2	29
10	BF3·Et2O (10)	48	rt	1:2	40
11	BF3·Et2O (10)	48	reflux	1:2	63
12	BF3·Et2O (10)	48	reflux	2:1	70
13d	BF3·Et2O (10)	48	reflux	2:1	79e

^aConditions: 0.40 mmol limiting reagent in CH₂Cl₂ (0.05 M), in glovebox.

^bDCE as solvent.

^cDetermined by GC relative to tetradecane as an internal standard.

^dConditions: 1a (2.0 mmol) and 2a (1.0 mmol) in CH₂Cl₂ (0.05 M), outside glovebox.

^eIsolated yield.