Diversity-Oriented Synthesis of Benzo[<i>f</i>][1,4]oxazepine‑, 2<i>H</i>‑Chromene‑, and 1,2-Dihydroquinoline-Fused Polycyclic Nitrogen Heterocycles under Microwave-Assisted Conditions

An efficient, diversity-oriented synthesis of oxazepino[5,4-<i>b</i>]quinazolin-9-ones, 6<i>H</i>-chromeno[4,3-<i>b</i>]quinolines, and dibenzo[<i>b</i>,<i>h</i>][1,6]naphthyridines was established involving a substrate-based approach under microwave-assisted and conventional heating conditions in high yields (up to 88%). The CuBr₂-catalyzed, chemoselective cascade annulation of <i>O</i>-propargylated 2-hydroxybenzaldehydes and 2-aminobenzamides delivered oxazepino[5,4-<i>b</i>]quinazolin-9-ones involving a 6-<i>exo</i>-<i>trig</i> cyclization-air oxidation-1,3-proton shift-7-<i>exo-dig</i> cyclization sequence. This one-pot process showed excellent atom economy (−H₂O) and constructed two new heterocyclic rings (six- and seven-membered) and three new C–N bonds in a single synthetic operation. On the other side of diversification, the reaction between <i>O</i>/<i>N</i>-propargylated 2-hydroxy/aminobenzaldehydes and 2-aminobenzyl alcohols delivered 6<i>H</i>-chromeno[4,3-<i>b</i>]quinolines and dibenzo[<i>b</i>,<i>h</i>][1,6]naphthyridines involving sequential imine formation-[4 + 2] hetero-Diels–Alder reaction-aromatization steps. The influence of microwave assistance was superior to conventional heating, where the reactions were clean, rapid, and completed in 15 min, and the conventional heating required a longer reaction time at a relatively elevated temperature.