Unanticipated Cleavage of 2-Nitrophenyl-Substituted N-Formyl Pyrazolines under Bechamp Conditions: Unveilingthe Synthesis of 2-Aryl Quinolines and Their Mechanistic Explorationvia DFT Studies

摘要

We herein report for the first time an unusual decomposition of 2-nitrophenyl-substituted N-formyl pyrazolines under Bechamp reduction condition employed to yield 2-aryl quinolines exclusively instead of pyrazolo[1,5-c]quinazolines. The reaction investigation suggests acid-mediated cleavage of >1 followed by a retro-Michael addition, and a subsequent in situ intramolecular reductive cyclization through a modified Friedlander mechanism afforded 2-aryl quinolines (>2) in good yields. The proposed mechanistic pathways were supported via experimental evidence and density functional theory studies. B3LYP/6-31+G(d) analysis indicated the involvement of trans-2-hydroxyaminochalcone as a key intermediate and its isomerization and cyclization, leading to unusual product formation.