Optimization of the reaction conditions^a.

Entry	Catalyst	Temperature (°C)	Solvent	Yieldb (%)
1	—	150	Toluene	18
2	—	150	Water	16
3	—	150	—	63
4	AgOTf	150	Toluene	84
5	Cu(OTf)2	150	Toluene	87
6	Sc(OTf)3	150	Toluene	50
7	AlCl3	150	Toluene	49
8	TfOH	150	Toluene	90
9	TMSOTf	150	Toluene	Quant.
10	TMSOTf	150	DCM	93
11	TMSOTf	150	MeCN	Quant.
12	TMSOTf	150	—	96
13	TMSOTf	100	—	92
14	TMSOTf	25	—	47
15	TMSOTf	200	—	75

^aReaction conditions: 1a (0.48 mmol, 1.0 equiv.), 2a (0.95 mmol, 2.0 equiv.), HMDS (2.38 mmol, 5.0 equiv.), catalyst (0.048 mmol, 0.1 equiv.).

^bIsolated yields.