Benzotropolone pigments

A theaflavin-related benzotropolone pigment having a procyanidin unit was synthesized in vitro. Although proanthocyanidin dimers have two B-rings, the condensation occurred regioselectively at the extension (upper) unit of the procyanidin due to steric effect. ... 

Matsuo, Y., Tanaka, T., and Kouno, I. 2006. A new mechanism for oxidation of epigal-locatechin and production of benzotropolone pigments. Tetrahedron 62 4774-83. 

Fomes fomentarius is a parasitic fungus of beech trees from which several benzotropolone pigments (42-45) and an unusual dicarboxylic acid (46) have been reported 33-36) (Chart 9). 

Chart 9. Benzotropolone pigments and a dicarboxylic acid from Pomes fomentarius References, pp. 17-20... 

Takino, Y., Imagawa, H., Horikawa, H., and Tanaka, A. 1964. Studies on the mechanism of the oxidation of tea leaf catechins. Part III. Formation of a reddish orange pigment and its spectral relationship to some benzotropolone derivatives. Agric. Biol. Chem. 28 64-71. 

---