2-Methoxy-3,6-dimethyl-4-hydroxybenzoic acid

Iso-rhizonic acid, 2-Methoxy-3,6-dimethyl-4-hydroxybenzoic acid (Iso-rhizoninsaure, 2-Methoxy-3,6-dimethyl-4-hydroxybenzoesaure)... 

Hydrolysis of the fourth isoprenyl benzoate (584) gave vanillic acid. Methylation of (584) afforded tomentellin (581). Thus, the structure of demethoxytomentellin was established to be 3,7-dimethyl-5-keto-2,6-octa-dienyl 3-methoxy-4-hydroxybenzoate (584). 

Hydroxybenzo[6]thiophene has been isolated from coal tar.42 It may be prepared from 6-aminobenzo[fr]thiophene by standard procedures.241 6-Methoxybenzo[h]thiophene may be prepared by decarboxylation of the corresponding 2-carboxylic acid,341 and 6-ethoxybenzo[6]thiophene is obtained by reduction of 6-(ethoxy)-thioindoxyl (Section VI, 1,2). 6-Methoxy-5-methylbenzo[6]thiophene is obtained by cyclization of (3-methoxy-4-methylphenylthio)-acetaldehyde dimethyl acetal (Section IV,B).617 The product previously described542 as 6-hydroxy-3-phenylbenzo[6]thiophene has now been shown to be the 2-phenyl isomer.307 6-Methoxy-818 and 6-methoxy-5-methyl-benzo[6]thiophene617 are demethylated by pyridine hydrochloride. 

Of the four monohydroxybenzo[c]cinnolines the 2- and the 4-isomers are potentially tautomeric with the corresponding quinonimines, e.g., 90 91. While the ultraviolet spectrum of 2-hydroxybenzo[c]cinnoIine shows close correspondence to that of the 2-methoxy compound in neutral solution, spectra of the conjugate acid and conjugate base both indicate appreciable charge-resonance between the 2- and 6-positions, and methylation of 90 with dimethyl sulfate or diazomethane gives rise to mixtures of 2-methoxy-benzo[c]cinnoline and the quinonimine 92. ... 

From 2-methoxy-3,6-dimethyl-4-benzyloxy-5-chlorobenzoic acid and methyl 2-methoxy-3,5,6-trimethyl-4-hydroxybenzoate with TFAA and subsequent debenzylation... 

---