The relative stereochemistry was assigned by a similar method
reported in Crich, D.; Banerjee, A. Acc. Chem. Res., 2007. 40, 151-
161. As a result of the shielding effect of the phenyl, the C-2 ester
group appeared in a more upfield domain in the endo configuration
when compared to the exo configuration.
In this reaction, Cu(I) and Cu(II) showed similar catalytic activity
minght be due to that Cu(II) would disproportionate into Cu(I) in
the reaction. Cu(I) might be the catalyticall active species in the reaction. 2002.