Cascade Annulation Enabled Access to Functionalized Polyaza Tetracycles With Fused Imidazo Scaffolds for Fluorescence “Turn‐Off” Sensing of Benzaldehyde Derivatives

Regioselective Ru(II)‐catalyzed C(sp 2 )─H activation with concomitant (4+2) cascade annulation materializes the benzimidazo‐ and imidazopyridine‐fused quinazolinyl ketones and quinazoline derivatives employing acyl azides and α‐azido ketones as the representative coupling surrogates. The insight of this protocol is established through control experiments and DFT analyses. Again, versatility is underscored by devising chemoselective imine bond reduction and directed nitro group functionalization ortho to the carbonyl moiety. In addition, bioactive ibuprofen‐appended benzimidazo‐quinazolinyl methanone analogue ( 3q ) and aspirin‐appended tetracyclic benzimidazo‐quinazoline analogue ( 5l ) have also been turned up, underscoring its potential significance as a novel pharmacologically relevant framework. Interestingly, a benzimidazo‐quinazoline derivative ( 5c ) showcased a pronounced fluorescence “turn‐off” response toward benzaldehyde and its substituted variant, with LODs of 2.03, 1.24, and 1.19 µM, respectively, exhibiting high sensitivity and selectivity.