Figure 3.

Reaction time course monitored by ¹H–¹⁵N NMR spectroscopy. (a) Representative time points from ¹H–¹⁵N HMBC experiments. Major correlations are highlighted using colored boxes on the spectra. (b) Construction of a reaction timeline on the basis of ¹H–¹⁵N HMBC experiments allows the design of additional NMR experiments to elucidate the structures of intermediates. (c) Structures of intermediates determined through the use of one- and two-dimensional NMR data.