Cascade Aza-Prins Reactions to Access Novel Fused Tetracyclic Heterocycles

Herein, we explore the scope and limitations of the BF3•Et2O-mediated alkyne aza-Prins reaction in tandem with an intramolecular Friedel-Crafts addition to synthesize tetracyclic molecules with both nitrogen and oxygen-containing heterocycles. We demonstrate its utility and versatility with the synthesis of numerous compounds containing a 7,8-dihydro-6H-chromeno[3,4-c]quinoline core. The use of aldehydes with varying electronic properties, ranging from both electron-donating to strongly electron-withdrawing, as well as varying substituents on the alkynyl substrates all afforded our desired target molecule in modest to good yields.