Rapid Access to Selenium-Containing Heterocycles Exhibiting Diverse Antimicrobial Activity via BF ₃ ·Et ₂ O-Mediated [3 + 3] Annulation

Organoselenium compounds possess unique properties and broad applications, yet their synthesis is less developed than that of oxygen or sulfur analogues. We report a BF₃·Et₂O-promoted [3 + 3] cyclization of selenocarboxamides with unsaturated ketones, enabling efficient access to diverse selenium-containing heterocycles, including indole- and benzofuran-fused selenazines. These frameworks, by incorporating selenium heteroatoms into carboline and thiazine, expand organoselenium structural diversity, and biological studies reveal potent, broad-spectrum antimicrobial activity, underscoring their potential as promising fungicide leads.