Facile preparation of dehydrodigallic acid and its derivative for the synthesis of ellagitannins.

A facile method for the synthesis of dehydrodigallic acid, which is a fundamental structure of ellagitannins, was developed. A classical Ullmann condition was effective for the formation of the highly hindered biaryl ether structure, and we clarified that the suitable protection of the phenolic hydroxy groups was crucial in this reaction. In this way, the synthesis of dehydrodigallic acid and its derivative was successfully performed. The described method would provide a synthetic utility toward ellagitannins.