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

An efficient, diversity-oriented synthesis of oxazepino[5,4- b ]quinazolin-9-ones, 6 H -chromeno[4,3- b ]quinolines, and dibenzo[ b , h ][1,6]naphthyridines was established involving a substrate-based approach under microwave-assisted and conventional heating conditions in high yields (up to 88%). The CuBr 2 -catalyzed, chemoselective cascade annulation of O -propargylated 2-hydroxybenzaldehydes and 2-aminobenzamides delivered oxazepino[5,4- b ]quinazolin-9-ones involving a 6- exo - trig cyclization-air oxidation-1,3-proton shift-7- exo-dig cyclization sequence. This one-pot process showed excellent atom economy (-H 2 O) 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 O / N -propargylated 2-hydroxy/aminobenzaldehydes and 2-aminobenzyl alcohols delivered 6 H -chromeno[4,3- b ]quinolines and dibenzo[ b , h ][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.