Depsidone synthesis. Part 21. A new synthesis of grisa-2′,5′-diene-3,4′-diones
Treatment of suitably substituted methyl 2-phenoxybenzoates with titanium(IV) chloride and dry hydrogen chloride afforded grisa-2′,5′-diene-3,4′-diones in high yield. The structures of these compounds followed from their thermal stability, their methanolysis to methyl 2-(4-hydroxyphenoxy)benzoates, and their reductive cleavage to 2,4′-dihydroxybenzophenones. Treatment of the benzophenones with base gave xanthones. An attempt to synthesize dehydrogriseofulvin (1) by this method failed.