Step 2: Synthesis of isoxazole-5-carbaldehyde
In a round bottom flask, isoxazol-5-yl-methanol (511 mg, 5.16 mmol) was dissolved in dichloromethane (30 mL). Dess-Martin periodate (2.3 g, 5.41 mmol) was added and the reaction mixture was stirred for 1.5 h at room temperature. Upon termination of the reaction, 50 mL of 10% aqueous Na2S2O3 and saturated aqueous NaHCO3 were added, followed by extraction with dichloromethane (2 x 30 mL). The organic layer was washed sequentially with saturated NaHCO3 aqueous solution, water and brine. The aqueous layer was back-extracted with dichloromethane. The organic layers were combined, dried over anhydrous sodium sulfate, filtered and concentrated. The residue was purified by silica gel column chromatography using EtOAc/hexane (gradient 0-40% EtOAc) as eluent to afford 226 mg (45% yield) of isoxazole-5-carbaldehyde as a colorless oil.1H NMR (CDCl3, 300 MHz) δ (ppm): 10.05 (s, 1H), 8.44 (d, J = 1.9 Hz, 1H). 7.02 (d, J = 1.9 Hz, 1H).
