Directed Lithiation反応を利用するAnthraquinone類の合成

抄録

A regiospecific synthesis of emodin trimethyl ether (12a), 7-hydroxyemodin tetramethyl ether (12b), helminthosporin trimethyl ether (12c), and chrysophanol dimethyl ether (12d) by use of directed lithiation strategy as a key step is described. The pathalides (7 and 9) were prepared by the condensation of the corresponding o-lithio benzamides (2) with benzaldehydes (3a and 3c) which were synthesized from m-cresol methoxymethyl ether by directed lithiation reaction. The phthalides (9) were then reduced to o-benzylbenzoic acids (10), which were easily converted to anthraquinones (12) by cyclisation with trifluoroacetic anhydride and subsequent oxidation with chromium trioxide.