Structure and synthesis of gymnopusin, a novel phenanthrenediol from the orchid Bulbophyllum gymnopus

Abstract

By the synthesis of 5,6,7-trimethoxyphenanthrene-2,10-diol (14) the structure originally proposed for gymnopusin is shown to be erroneous. Reinterpretation of the spectroscopic data for gymnopusin led to the proposal of a revised structure 3,4,9-trimethoxyphenanthrene-2,7-diol (31) which was confirmed by synthesis. The key step in the synthesis of these 9(10)-oxygenated phenanthrenes was a Pummerer rearrangement.