Although pimpinellin has been known for many years, synthesis of the compound has not been reported. A useful intermediate toward the synthesis of pimpinellin would be 2-carboxy-6-methoxy-4,7-benzofurandione or its ester. These have been synthesized from pyrogallol in an eight step synthesis via methyl 4,6,7-trimethoxy-coumarilate. However, there is some question of the structure of two of the intermediate compounds in this sequence. The projected approach was to attempt to form this same benzofurandione in fewer steps from the same starting material by oxidation of the more readily available 6,7-dimethoxycoumarilic acid or its ester. Neither this acid nor its ester formed the quinone on oxidation with nitric acid nor lead tetraacetate, but underwent nitration instead. The 5-bromo acid and ester were not oxidized with nitric acid. Selective demethylation of the 7- methoxy group of 6,7-dimethoxycoumarilic acid was attempted. Fremy's salt or lead tetraacetate might be used to oxidize this cleavage compound to the corresponding 4,7-quinone. Unfortunately, the cleavage product was not obtained.

It has been over forty years since pimpinellin was isolated pure and its structure determined. We wished to explore possible routes for its total synthesis, unknown to this time. One route was via methyl 5-formyl-4,6,7-trimethoxycoumarilate. The route of Paul was reexamined through cleavage of 2,3,4,6-tetramethoxy-benzaldehyde to 2-hydroxy-3,4,6-trimethoxybenzaldehyde and its condensation to 4,6,7-trimethoxycoumarilic acid. Paul reported low yields and difficult purification steps. We were able to isolate the compounds pure but in too low yields to warrant further work at this time. Evidence suggests the synthesis of methyl 5-formyl-4,6,7-trimethoxycoumarilate, but lack of starting material and time prevented further examination now. An alternate route, via dihydrocinnamic acids followed by oxidation to quinones and reduction, would provide a needed phenolic group. We found that 2,3,4-trimethoxydihydrocinnamic acid and its ester did not form a quinone on oxidation, but ethyl 2,3,4,6-tetramethoxydihydrocinnamate did form a quinone on oxidation with chromic acid or argentic oxide.