[2,3,6-trioxypentafulvenes .5(1). Reactions With Primary Amines - Nucleophilic-substitution and Ring Expansion]

The reaction between dimethyl 2,3,6-trihydroxypenta-fulvene- 1,4-dicarboxylate and primary alkyl or cycloalkylamines (methylamine, butylamine, cyclooctylamine, cyclohexylamine) affords the corresponding 6-aminopentafulvenes (nucleophilic substitution of the C6 hydroxyl group by the amine) or dimethyl 5-amino-2,3-dihydroxyterephthalates (ring expansion) depending on the reaction conditions. For the two kinds of compounds both a spectroscopic study and a single crystal X-ray analysis have been carried out. Different hydrogen bondings have been observed. Only the substitution products are obtained in the reaction between dimethyl 2,3,6-trihydroxypentafulvene-1,4-dicarboxylate and primary aromatic amines (aniline, 4-sec-butylaniline, p-anisidine). When p-nitroaniline or p-aminobenzonitrile are used the reaction does not progress.