A novel synthetic approach toward 4-formyl-7-hydroxyindoles and 4, 7-indoloquinones is described. Basically, two major operations need to be carried out, namely:(1) ozonization of the appropriately protected 4-amino-5-hydroxyindenes leading eventually to 4-formyl-7- hydroxyindoles and (2) Fremy's salt promoted oxidative degradation of the later compounds to the desired 4, 7-indoloquinones. A formal synthesis of PDE I and PDE I1 has been ...
