3-Aryltetronic acids: efficient preparation and use as precursors for vulpinic acids.

3-Aryltetronic acids were prepared in one step by treatment of a mixture of methyl arylacetates and methyl hydroxyacetates with potassium tert-butoxide, via tandem transesterification/Dieckmann condensation. Several mushroom or lichen pigments, vulpinic acids, were synthesized from 3-(4-methoxyphenyl)tetronic acid in three steps involving the reaction of the corresponding dianion with an α-ketoester and the dehydration of the tertiary alcohols obtained into mixtures of (E)- and (Z)-alkenes, which were converted under UV irradiation at 254 nm to natural (E)-isomers. Syntheses of pinastric acid, 4,4′-dimethoxyvulpinic acid, and the first synthesis of recently isolated methyl 3′,5′-dichloro-4,4′-di-O-methylatromentate were hence achieved in an efficient manner.