Synthesis of Functionalized Benzo[h]Quinolines via Base-Catalyzed 1,4-Addition/Intramolecular Annulation Cascade

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Medicinal Chemistry

Background:

• Benzo[h]quinoline (BhQ) is a crucial scaffold in natural products and synthetic compounds.
• Existing BhQ synthesis methods are often multi-step, require harsh conditions, and are time-consuming.

Purpose of the Study:

• To develop an atom- and step-economical one-pot synthesis for functionalized BhQs.
• To explore the scope and limitations of the new synthetic methodology.
• To elucidate the reaction mechanism and understand regioselectivity.

Main Methods:

• Lithium-hexamethyldisilazane-catalyzed double annulation cascade reaction.
• Utilized benzonitriles and diynones as starting materials.
• Employed density functional theory (DFT) calculations to propose a reaction mechanism.

Main Results:

• Successfully synthesized thirty-four functionalized BhQs in up to quantitative yields.
• Investigated substrate scope, revealing electronic and steric influences on reactivity and regioselectivity.
• Demonstrated gram-scale synthesis and functional group modification of BhQ derivatives.

Conclusions:

• The developed one-pot approach offers an efficient and economical route to complex BhQ structures.
• The findings provide valuable insights into the reaction mechanism and regioselectivity.
• The method facilitates the construction of diverse BhQ derivatives for synthetic and pharmaceutical applications.