Metal and Base-Free Synthesis of Benzoxazino and Benzoxazepino Fused Isoquinolines: A DFT Insight and Photophysical Study

A novel metal- and base-free approach for the synthesis of benzoxazino and benzoxazepino fused isoquinoline derivatives from ortho-alkynyl aldehydes and amines under mild reaction conditions has been described. The formation of new C−O and C−N bonds via metal-free cyclization with internal alkyne aided by water molecules without using external ligands and bases has been described. In addition, a series of control experiments are performed, and mechanistic studies are discussed elaborately by Density Functional Theory (DFT) calculation. Furthermore, gram-scale synthesis and photophysical studies of the synthesized compounds and their quantum yield calculation have been demonstrated.