Synthesis of Pyridocarbazole Alkalois by Using Reactity of Anhydride

Abstract

Indole-2,3-dicarboxylic anhydride is an attractive intermediate in a synthesis of natural products. We have shown the synthesis of ellipticine by the reaction of 1-benzylindole-2,3-dicarboxylic anhydride (1) with 3-bromo-4-lithiopyridine. Recently, reaction of 1-benzylindole-2,3-dicarboxylic anhydride (1) with anisoles in the presence of titanium chloride (IV) gave 3-(4-methoxybenzoyl)indole-2-carboxylic acids as sole products in high yields. However, in a similar manner, reaction of 1-benzenesulfoylindole-2,3-dicarboxylic anhydride with anisoles afforded 2-(4-methoxybenzoyl)indole-3-carboxylic acids, exclusively. In this report, we would like to show a synthesis of pyridocarbazole alkaloids, ellipticine and olivacine, by the reaction of the anhydride with 2,4,6-trimethoxypyridine in the presence of titanium chloride (IV).