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.