Solvent-Controlled [4 + 2] Annulation Reaction: Selective Synthesis of 1,4-Dihydroquinolines/Quinolines

Area of Science:

• Organic Chemistry
• Synthetic Chemistry

Background:

• Quinolines and 1,4-dihydroquinolines are important heterocyclic scaffolds.
• Efficient synthesis of these compounds often requires metal catalysts or harsh conditions.

Purpose of the Study:

• To develop a selective and practical synthesis for 1,4-dihydroquinolines and quinolines.
• To achieve this synthesis using readily available reagents and mild conditions.

Main Methods:

• Utilizing a [4 + 2] annulation reaction between aminobenzyl phosphonium salts (ABPS) and enaminones.
• Employing solvent control (THF or DMSO) to selectively yield either 1,4-dihydroquinolines or quinolines.
• Avoiding the use of metal catalysts and basic additives.

Main Results:

• Achieved selective synthesis of 1,4-dihydroquinolines in THF.
• Achieved selective synthesis of quinolines in DMSO.
• Demonstrated excellent substrate generality and high yields under mild conditions.

Conclusions:

• Developed a metal-free, catalyst-free annulation strategy for quinoline synthesis.
• Solvent-controlled synthesis offers a practical and efficient route to diverse 1,4-dihydroquinolines and quinolines.
• The method is amenable to scale-up due to readily accessible reagents and mild conditions.