Dziewonski et al., Bulletin International de l'Academie Polonaise des Sciences et des Lettres, Classe des Sciences Mathematiques et Naturelles, Serie A: Sciences Mathematiques, 1937, p. 555,566
Condensation of 2-hydroxyacetophenone with benzaldehyde in the presence of 70% perchloric acid in ethylorthoformate gave the corresponding 4-ethoxyflavylium perchlorate, which was treated with aqueous ammonia or methylamine solution to afford 1,6,7,8-substituted 2-(3′,4′-substituted-phenyl)-4-quinolone in fair to good yield.