Hydrochloric Acid → 3-hydroxy-5-[(1S)-2-methoxy-1-methylethoxy]benzoic acid

Participants

Reaction Conditions

Reaction Steps

To a flask fitted with overhead stirrer, condenser, thermometer and nitrogen line was added methyl 3-hydroxy-5-[(phenylcarbonyl)oxy]benzoate (1.0 eq), cesium carbonate (1.5 eq) and dimethylsulfoxide (7.0 vols) under a nitrogen atmosphere. The batch was heated to 40-45° C. (1R)-2-methoxy-1-methylethyl 4-methylbenzenesulfonate (1.3 eq) was added slowly dropwise over at least 90 minutes maintaining reaction temperature at 40-45° C. The reaction mixture was held for at least 8 hours and then was cooled to 15±4° C. Iso-propyl acetate (4.0 vols) was added followed by water (5.0 vols), keeping the reaction temperature below 25° C. The reaction mixture was agitated for approximately 15 minutes and then the layers were separated. The organic phase was retained. The aqueous phase was re-extracted with further iso-propyl acetate (3 vols). The reaction mixture was agitated for approximately 15 minutes and then the layers separated. This process was repeated with further isopropyl acetate and the organic phases were combined and then washed with water (3 vols). After approximately 15 minutes agitation the layers were separated, and water (3 vols) was added to the organic layer. After approximately 15 minutes agitation the layers were separated and the organic layer was vacuum distilled at 40° C. until no more solvent could be distilled. Methanol (7 vols) was added, then sulphuric acid (0.8 eq) was added and the mixture was heated to reflux for at least 16±4 hours. The reaction mixture was vacuum distilled at 40° C. until a pot volume of 2.5-3 vols was achieved. Toluene (4 vols) was added to the flask, and vacuum distillation continued at 35° C. until a pot volume of 4.0 vols was achieved. The mixture was cooled to 20±5° C. Water (15 vols) was added to the reaction mixture and the mixture agitated at 20±5° C. for at least 15 minutes. The batch was separated and the organic layer was cooled to 0-5° C., before 0.5M sodium hydroxide (1.0 eq) was added slowly keeping the batch temperature below 5° C. The vessel was agitated for 15 minutes and then separated. The aqueous layer was retained and the organic layer was treated with 0.5M sodium hydroxide (1.0 eq; added slowly keeping the batch temperature below 5° C.). The vessel was agitated for 15 minutes and then the layers were separated. The aqueous layers were combined and toluene (3 vols) added slowly keeping the batch temperature below 5° C. The vessel was agitated for 15 minutes and then separated. The aqueous layer was warmed to 25±5° C., and 33% w/w sodium hydroxide added (0.5 eq). After 2 hours stirring, 37% w/w hydrochloric acid (2.1 eq) was added to adjust the pH to pH 2. Methyl tert-butyl ether (3 vols) was added, the mixture was agitated for 15 minutes, then the layers separated. The organic layer was retained. The aqueous layer was re-extracted with MTBE (3 vols) and the combined organic layers were distilled under vacuum at 35° C. to a pot volume of approximately 3 vols, collecting 3 vols distillates. Toluene (5 vols) was added, and the batch temperature adjusted to 50° C. Water (1 vol) was added and the batch agitated for at least 15 minutes at this temperature then the layers were separated. The organic layer filtered through a filter then distilled at 35° C. until the mixture became turbid. The material was cooled to 20° C., seeded with 3-hydroxy-5-[(1S)-2-methoxy-1-methylethoxy]benzoic acid and agitated at this temperature for 3 hours. The mixture was then distilled under vacuum at 25° C. is removing further MTBE, and then cooled to 5° C. for at least 2 hours. The mixture was filtered, and the solid was washed with toluene (1 vol) at 20° C. The batch was dried with vacuum or under a stream of nitrogen until constant weight was attained at 20° C. After drying, the title compound was obtained as a solid (corrected yield typically 40-50%). 1H NMR δ (400 MHz DMSO): 12.82 (bs, 1H), 9.74 (bs, 1H), 6.95 (bs, 1H), 6.91 (bs, 1H), 6.56-6.55 (t, 1H), 4.59-4.52 (m, 1H), 3.5-3.41 (m, 2H), 3.28 (s, 3H), 1.21-1.19 (d, 3H).

Provenance & Evidence