Table 2.

Tested conditions for cyclization precursor 14.

Entry	Lewis acid	Conditions	Product (Yield[a])
1	B(C6F5)3 (2.5 mol%)	CH2Cl2, 30 °C, 8.5 h	15 (77 %)
2	SnCl4 (1.1 equiv.)	CH2Cl2, −78 °C to 0 °C, 2 h	15 (25 %), 16 (19 %)
3	SnCl4 (10 mol %)	CH2Cl2, −78 °C to 0 °C, 4 d	15 (21 %), 16 (15 %), 14 (36 %)
4	SnCl4 (20 mol %)	CH2Cl2, −78 °C to 0 °C, 2 d	15 (26 %), 16 (<5 %)
5	SnCl4 (30 mol %)[b]	CH2Cl2, −78 °C to 0 °C, 6 h	15 (43 %), 16 (1 %)
6	SnCl4 (1.1 equiv.)	toluene, −78 °C to 0 °C, 4 d	15 (45 %)
7	SnCl4 (1.1 equiv.)	CHCl3, −78 °C to 0 °C, 4 h	15 (37 %), 16 (<5 %)

[a] Isolated yield. [b] 0.1 equiv. were added every two hours.