Synthesis
General procedure for the synthesis of 4-hydroxy-6-methoxyquinoline-3-carboxylic acid from 4-hydroxy-6-methoxyquinoline-3-carboxylic acid: 4-hydroxy-6-methoxyquinoline-3-carboxylic acid (7, 15.7 g, 72 mmol) was dissolved in 80 mL of diphenyl ether and heated to 245 °C in a metal bath for 2 hours. After completion of the reaction, the mixture was cooled to room temperature and dissolved in 200 mL of hexane. The mixture was stirred for 3 hours and then filtered. The resulting solid was washed with ethyl acetate and dried to give 6-methoxyquinolin-4-ol (8, 12.5 g, 72 mmol, 100% yield). The product was characterized by 1H-NMR (DMSO-d6): δ= 3.81 (s, 3H), 5.99 (d, 1H), 7.28 (dd, 1H), 7.48-7.53 (m, 2H), 7.86 (d, 1H), 11.87 (bs, 1H).Results of the LC-MS analysis: retention time (Rt) = 0.87 min; mass spectrum (MS): m/z = 176 [M + H]+.
References
[1] Tetrahedron Letters, 2017, vol. 58, # 8, p. 794 - 796
[2] Journal of the American Chemical Society, 1946, vol. 68, p. 1204,1206
[3] Organic Syntheses, 1955, vol. Coll. Vol. III, p. 272
[4] Journal of the American Chemical Society, 1947, vol. 69, p. 1659,1660
[5] Chemical and Pharmaceutical Bulletin, 2007, vol. 55, # 5, p. 821 - 824
