SnCl₂-mediated heterocyclization approach for the synthesis of benzisoxazole/quinoline-embedded β-carboline scaffolds

A Sn(II)-mediated facile entry towards construction of C-C/C-O and C-C/C-N bonds was devised. The developed reductive heterocyclization method is described for the synthesis of a diverse range of novel β-carboline C-1- and C-3-linked vinyl benzisoxazole analogues from the corresponding 2-nitro chalcones. In addition, the synthesis of β-carboline C-1-substituted quinolines (Nitramarine analogues) was achieved. The protocol was extended towards the formation of quinoline C-3-substituted benzisoxazole derivatives in good yields utilizing 2-alkynyl-3-formyl quinolines and 2-nitroacetophenone as templates. The scope of our strategy was demonstrated with the synthesis of a library of 56 novel molecules. The synthesized benzisoxazole derivatives had light-emitting properties to deliver a fluorescence quantum yield up to 33%.