Optimization of the reaction conditions^a.

Entry	Acid	Solvent	Yieldsb (%)
			2a	3a
1	TMSOTf	DCM	50	44
2	TMSOTf	Toluene	48	43
3	TMSOTf	THF	56	33
4	TMSOTf	MeCN	44	<5
5	AgOTf	DCM	44	17
6c	(CuOTf)2·toluene	DCM	N.R.	N.R.
7	Cu(OTf)2	DCM	58	15
8	Sc(OTf)3	DCM	52	24
9	Bi(OTf)3	DCM	47	30
10	Fe(OTf)3	DCM	52	30
11	In(OTf)3	DCM	62	20
12	Ac2O	DCM	N.R.	N.R.
13	AlCl3	DCM	23	__d
14	BF3·OEt2	DCM	31	20
15	AcOH	DCM	52	20
16	TfOH	DCM	50	23
17c	p-TsOH	DCM	N.R.	N.R.

^aReaction conditions: 1a (1.0 mmol), HMDS (0.5 mL, 2.4 mmol), acid (0.5 mmol), solvent (2 mL), MW (150 °C), 0.5 h.

^bIsolated yields.

^cNo reaction occurred.

^dUnknown products were obtained.