Intramolecular aldol-type condensation between side chains of naphthoquinones: biomimetic synthesis of 1,6- and 1,8-dihydroxyanthraquinones

Abstract

Intramolecular condensation of 2-(acetonyl)-3-acyljuglone derivatives under basic conditions gave 1,6- and/or 1,8-dihydroxyanthraquinones depending on the conditions employed. Treatment of 6-[(3-acetyl-5-methoxy-1,4-dioxo-1,4-dihydro-2-naphthyl)methyl]-2,2-dimethyl-4H-1,3-dioxin-4-one with K₂CO₃ in alcohol brought about the intramolecular Knoevenagel-type reaction to give 3-hydroxy-8-methoxy-1-methyl-9,10-dioxo-9,10-dihydro-anthracene-2-carboxylates in good yields, while the same naphthoquinone gave 4-hydroxy-5-methoxy-9,10-dioxo-9,10-dihydroanthracene-2-acetic acid in good yield by treatment with potassium bis(trimethylsilyl)amide (KHMDS). Chrysophanol, aloe-emodin, aloesaponarin I, and K1115A were prepared in good yields.