Synthetic Studies on Lignans and Related Compounds. IV. Synthesis of Taiwanin C and E, and Justicidin D (Neojusticin A), E, and F (Taiwanin E Methyl Ether)

Abstract

The structure of taiwanin E was re-examined with an empirical proton magnetic resonance (¹H-NMR) rule for the lactone methylene in aromatized naphthalide lignans, and concluded to be 5 instead of 4 on the basis of their unambiguous synthesis. Related lignans : taiwanin C (3), justicidin D (neojusticin A) (6), E (7), and F (taiwanin E methyl ether) (8) were also synthesized. The ¹H-NMR rule was found to be the case also with the lignans synthesized.