Fig. 3
1H NMR spectrum of intermediates 5. a NOE and 1H NMR for intermediates 5a. The red arrow indicates the peaks of intermediate 5a-1. The black arrow indicates the peaks of intermediate 5a-2. The blue arrow indicates the peaks of intermediate 5a-3. b MS data for intermediates 5a (LC–MS analysis using MeOH as a solvent)
