First Total Synthesis of the Benzotropolone/Bis(pulvinone) Natural Product Aurantricholone Exploiting New Strategies for Establishing Benzotropolones andZ‐Configured Pulvinones

Abstract

AbstractAurantricholone as well as its calcium and lithium salts, all of which represent the coloring principle of the fungusTricholoma aurantium, were synthesized for the first time, namely in 15 steps, 10 of which were our longest linear sequence. We developed an access to benzotropolones after dibromocyclopropanating alkyl or silyl enol ethers of 1‐tetralones. Successive treatments with DMAP‐N‐oxide and Ac2O effected ring‐enlargement, oxidation, and acetylation.O‐acetyl‐1‐bromo‐3,4‐dimethoxybenzotropolone obtained thereby – similarly as unsubstituted benzotropolone – was brominated at C‐8 in two steps by adopting our recently published bromination protocol for otherwise unsubstitutedO‐acetylbenzotropolone. Thereafter, a double and doublyZ‐selective Suzuki‐coupling with a newly introduced boronate established theO‐methylated pulvinone moiety as well as theO‐methylated “pulvinone‐like” motif of what altogether equaled the completed aurantricholonescaffold. Its deprotection (two steps) furnished the title compound either as its protonated form or its calcium or lithium salt.