sentences:  Further studies and reviews of the Combes quinoline synthesis and its variations have been published by Alyamkina "et al"., Bergstrom and Franklin, Born, and Johnson and Mathews.The Combes quinoline synthesis is often used to prepare the 2,4-substituted quinoline backbone and is unique in that it uses a β-diketone substrate, which is different from other quinoline preparations, such as the Conrad-Limpach synthesis and the Doebner reaction.The reaction mechanism undergoes three major steps, the first one being the protonation of the oxygen on the carbonyl in the β-diketone, which then undergoes a nucleophilic addition reaction with the aniline.