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Canter, Robertson, and Waters : Lichen Acids. Part V . 493 123. Lichen Acids. Part V. A Synthesis of Methyl 0-Tetramethylgyro p h r a t e. THE synthesis of o-diorsellinic acid by Fischer and Fischer (Ber., 1913, 445, 1138; 1914, 47, 505) disproved the suggestion of Hesse ( J . pr. Chm., 1900, 62, 463) that the lichen product gyrophoric acid, which occurs in the majority of species of Gyrophora, was a didepside isomeric with lecanoric acid. More recently, Asahina and his co-workers ( J . Pharm. SOC. Japan, 1925, No. 519, 1 ; Ber., 1930, 63, 3044; 1932, 65, 983) have shown that the compound is a tridepside composed of three units of orsellinic acid, and, starting from lecanoric acid, have effected a synthesis of methyl tetramethylgyrophorate. In a similar manner, using the requisite diacetate of lecanoric acid, Koller (Monatsh., 1932, 61,