Synthesis of 8-fluororhein

Abstract

8-Fluoro-5-methoxy-1-tetralone has been formylated, aromatised and alkylated to give 8-fluoro-1-isopropoxy-5-methoxy-2-naphthaldehyde 11. Condensation of this with a phosphonosuccinate gave, after deprotection, the 4-naphthylbutenoic acid which was cyclised and methylated to give the ethyl 9-fluoro-10-isopropoxy-4, 6-dimethoxy-2-carboxylate 12. Removal of the isopropyl group, dichromate oxidation and deprotection gave 8-fluorohein 3, an analogue of the osteoarthritis drug rhein.