Ebenaceae extractives. Part 11. The synthesis of 7-methyljuglone. A re-examination

Abstract

The Friedel–Crafts reaction between maleic anhydride and 4-chloro-3-methylphenol yields, besides 8-chloro-5-hydroxy-7-methylnaphthoquinone 1, helminthosporin 5 and its 8-chloro derivative 6 and, after methylation, methyl (E)-β-(5-chloro-2-methoxy-4-methylbenzoyl)acrylate 4. Treatment of the chloronaphthoquinone 1 with tin(II) chloride in hydrochloric acid and tetrahydrofuran followed by iron(III) chloride converts it efficiently into 7-methyljuglone 2.