Table 7.

Additive screening.

Entry	Additive	Equivalent	Yield 4a (%)b	Yield 10 (%)b
1	–	–	53	8
2	MS 4 Å	50 mg/0.1 mmol	51	<5
3	TMSCl	1 equiv	40	–
4	TFAA	1 equiv	54	–
5	(TMS)2O	1 equiv	48	13
6	BF3·Et2O	1 equiv	75	–
7	B(OTFE)3	1 equiv	53	10
8	BF3·Et2O	2 equiv	37	n.d.
9	BF 3 ·Et 2 O	0.3 equiv	72	9
10	BF3·Et2O	0.1 equiv	67	13

^aThe data were already published in the supporting information of Ref. [45] except for the yield of 10 and for entry 10. ^bNMR yield determined using CH₂Br₂ as internal standard. n.d. = not determined.