The effect of various Lewis acids.

Entry	RX	Lewis acid	Product	Yield [%]
1a	282	ZnCl2	283	99
2a	279	ZnCl2	541	—
3b	279	AgOTf	541	81
4a	540	ZnCl2	542	Tracec
5b	540d	AgOTf	542	—

^aReaction condition: ZnCl₂ (10 equiv.), RX (2 equiv.), Et₂O, 0 °C.

^bReaction condition: AgOTf (4 equiv.), RX (3 equiv.), THF, −78 °C.

^cComplex mixture.

^d540 two equivalents. Reaction temperature: −78 to 0 °C.