The 1H NMR spectra of 6e in CDCl3 showed two doublet of doublet
(dd) peaks at δ 2.94 ppm and 3.00 ppm, corresponding to the two
diastereotopic methylene protons Ha and Hb, respectively, as
shown in Fig. 1. Ha showed a doublet of doublet peak caused by coupling
with the germinal proton Hb with 2J =12.44 Hz, then with the
vicinal proton Hc (α-proton) with 3J=4.40 Hz. Similarly, Hb showed
a doublet of doublet peak as a result of coupling with the germinal
proton Ha with 2J = 12.30 Hz, then with the vicinal proton Hc (α-
proton) with 3J = 4.44 Hz. Also, two singlet peaks at δ 3.65 ppm
and 3.72 ppm corresponding to the methyl ester group, and another
two singlet peaks at δ 3.89 ppm and 3.91 ppm corresponding to the
two methoxy groups were observed. A multiplet peak appeared at
δ 5.00–5.03 ppm and δ 6.39 ppm corresponding to the α-proton
and NH respectively was observed.