Synthesis of 8-Phenylphenalenones: 2-Hydroxy-8-(4-hydroxyphenyl)-1H-phenalen-1-one from Eichhornia crassipes.

2-Hydroxy-8-(4-hydroxyphenyl)-1H-phenalen-1-one (1), the first reported 8-phenylphenalenone from the roots of Eichhornia crassipes (water hyacinth), was synthesized starting from 2-methoxynaphthalene in 11 steps and with an overall yield of 2%. A cascade Friedel-Crafts/Michael annulation reaction between acryloyl chloride and 2-methoxynaphthalene afforded 9-methoxyperinaphthanone that, after transformation to 9-methoxy-2-(4-methoxyphenyl)-1H-phenalen-1-one by means of standard Suzuki-Miyaura methodology, was subjected to a reductive carbonyl transposition to afford 8-(4-methoxyphenyl)perinaphthanone. Dehydrogenation, epoxidation, and demethylation of the latter afforded 1.