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. 2014 Mar 12;16(6):1826–1829. doi: 10.1021/ol500390a

Table 1. Identifying of a Suitable Lewis Acid.

graphic file with name ol-2014-00390a_0008.jpg

entry LA solvent temp (°C) time (h) yielda (%) dr ratiob
1 EtAlCl2 CH2Cl2 –78 12 14 N.D.c
2 AlCl3 CH2Cl2 –78 12 38 60:(20:20)
3 BF3–OEt2 CH2Cl2 –78 12 33 N.D.
4 TMSOTf CH2Cl2 –78 12 48 34:(33:33)
5 SnCl4 CH2Cl2 –78 12 60 68:(16:16)
6 TiCl4 CH2Cl2 –78 12 52 68:(16:16)
7 MgBr2 THF rt 14 no rxnd  
8 Zn(OTf)2 CH2Cl2 rt 18 no rxn  
9 Yb(OTf)3 CH2Cl2 rt 15 no rxn  
10 La(OTf)3 CH2Cl2 rt 15 no rxn  
a

Isolated yields; in all cases, 1.0 equiv of Lewis acid was used.

b

Ratios denote endo:exo with exo-I:exo-II ratios shown in parentheses. All ratios determined using 1H and/or 13C NMR.

c

N.D. = not determined.

d

Complete recovery of the starting diene 1.