General procedure for the synthesis of ethyl 5-tert-butyl-isoxazole-3-carboxylate from the compound (CAS:94122-76-6): tert-butyl alkenone (50) (6.00 g, 30.0 mmol) was dissolved in anhydrous ethanol/THF (1:1, 70 mL) and stirred at room temperature. To this solution was added hydroxylamine hydrochloride (2.29 g, 33.0 mmol) and the resulting mixture was stirred under nitrogen protection for 12 hours. Subsequently, the mixture was transferred to a Soxhlet extractor fitted with molecular sieves and heated to reflux for 2 hours. After completion of the reaction, the mixture was allowed to cool and the solvent was removed by evaporation. Water (100 mL) was added and the mixture was extracted with dichloromethane (2 x 100 mL). The organic phases were combined, dried over anhydrous sodium sulfate and concentrated. The crude product was purified by silica gel column chromatography to afford ethyl 5-tert-butyl-isoxazole-3-carboxylate (54) as a colorless oil (3 g, 51% yield).1H NMR (500 MHz, CDCl3) data for 54: δ 6.37 (s, 1H), 4.43 (q, 2H), 1.41 (t, 3H), 1.37 (s, 9H).
