Regioselective Synthesis of Benzo[h][1,6]- naphthyridines and Chromenopyrazinones through Alkyne Cyclization

A regioselective approach to the synthesis of benzo[h][1,6]-naphthyridine and chromenopyrazinone derivatives was developed. The synthetic route to benzo[h][1,6]naphthyridines involves the N-propargylation of aromatic aminobenzaldehydes, followed by reaction with propargylamine in the presence of DBU (1,8-diazabicyclo[5.4.0] undec-7ene). For the synthesis of chromenopyrazine and chromeno-pyrazinone derivatives, the acetonitrile group was introduced to salicylaldehyde derivatives, and a DBU-promoted cyclization reaction between aldehydes and propargylamine gave the chromenopyrazines. The intramolecular heterocycloaddition reaction between the triple bond and the azadiene, which is formed as an intermediate, gave the desired structures.