The general procedure for the synthesis of 4-hydroxy-6-methoxyquinolin-2-one from the compound (CAS:15589-58-9) is as follows: diphenylamine (1.0 eq.) was placed in a round-bottomed flask and 10 times (by weight) polyphosphoric acid was added to form a syrupy mixture. The mixture was heated at 130-140°C for 6 hours. Upon completion of the reaction, the mixture was slowly poured into crushed ice and alkalized with 4N NaOH solution. The solid product was collected by filtration and the remaining liquid was transferred to a partition funnel and washed with ether (3 x 5 mL). The aqueous phase was transferred to a beaker in an ice bath and acidified with 6N HCl to pH=1 to induce precipitation of 4-hydroxy-3,4-dihydro-1H-quinolin-2-one. The solid product was collected by filtration through a Brinell funnel, washed several times with deionized water, and subsequently placed in a desiccator and dried under vacuum for 24 hours using P2O5 as the desiccant. The resulting product can be used for subsequent reactions without further purification.
References
[1] Tetrahedron, 1989, vol. 45, # 3, p. 757 - 762 [2] European Journal of Medicinal Chemistry, 2014, vol. 81, p. 253 - 266
