4-Quinolone is an organic compound derived from quinoline. It and 2-quinolone are the two most important parent (meaning simplified) quinolones. 4-Quinolone exists in equilibrium with a minor tautomer, 4-hydroxyquinoline (CAS#611-36-9). Aside from pedagogical interest, 4-quinolone is of little intrinsic value but its derivatives, the 4-quinolone antibiotics, represent a large class of important drugs.[1]

The tautomeric equilibrium relating 4-quinolone (right) and 4-hydroxyquinoline (left)

Synthesis

The chemical synthesis of quinolones often involves ring-closing reactions.[2] Such reactions often install a hydroxyl group (an –OH functional group) on the carbon across from the ring nitrogen (i.e., the C-4 positions). An example of such a synthesis is the Camps cyclization, which, depending on starting materials and reaction conditions, can give both 2-hydroxyquinolines (B) and 4-hydroxyquinolines (A) as shown. The hydroxyquinolines tautomerize to the quinolones.

The Camps cyclization, a quinoline synthesis giving 2- and 4-hydroxyquinolines.
The Camps cyclization, a quinoline synthesis giving 2- and 4-hydroxyquinolines.

References

  1. ^ Andriole, VT The Quinolones. Academic Press, 1989.
  2. ^ Shi, Pengfei; Wang, Lili; Chen, Kehao; Wang, Jie; Zhu, Jin (2017). "Co(III)-Catalyzed Enaminone-Directed C-H Amidation for Quinolone Synthesis". Organic Letters. 19 (9): 2418–2421. doi:10.1021/acs.orglett.7b00968. PMID 28425721.