Selective synthesis of 5,6-dihydrophenanthridines, 5,6-dihydrobenzo[c][1,8]naphthyridines and their fully aromatized analogues via the Pictet-Spengler reaction mediated by peptide coupling agent propylphosphonic anhydride (T3P)

A new method has been developed for the selective synthesis of 5,6-dihydrophenanthridines, 5,6-dihydrobenzo[c][1,8]naphthyridines and their fully aromatized analogues via the Pictet-Spengler reaction mediated by propylphosphonic anhydride (T3P). The method, which uses less toxic and readily available T3P, generally seems to be more flexible, efficient in the preparation of 5,6-dihydrophenanthridine derivatives and complementary to conventional routes in the preparation of fused pyridines.