SOLUBLE CATALYSTS FOR IMPROVED PSCHORR CYCLIZATIONS

Several improved catalysts for the Pschorr phenanthrene synthesis have been discovered; all are soluble substances which initiate free-radical reactions by electron donation and thereby shorten the reaction time and increase the yield. One technique with K4Fe(CN)(6) in water produced phenanthrene-9-carboxylic acid (6a) in 87% yield, but its application did not extend to substituted examples where the diazonium salt is less soluble in water. A more general procedure with ferrocene in acetone produced not only 6a but also substituted examples 6b-f in yields of 88-94%. A modification which avoids the isolation of diazonium salts was developed for occasional synthetic use.