General procedure for the synthesis of 3,5-dimethylisoxazole from acetylacetone: To a solution of hydroxylamine hydrochloride (8.34 g, 0.12 mol) in water (10 ml) was slowly added a solution of 2,4-pentanedione (6) (10.2 g, 0.1 mol) in ethanol (10 ml). The reaction mixture was heated to reflux at set temperature for 3 hrs and subsequently cooled to room temperature and slowly poured into cold water (60 ml). The mixture was extracted using ether (3 x 40 ml). All the organic layers were combined and dried with anhydrous sodium sulfate (Na2SO4) followed by evaporation under reduced pressure to remove the solvent to give a brown oily residue. The residue was purified by reduced pressure distillation to afford 3,5-dimethylisoxazole (5) (8.10 g, 82% yield) as a colorless liquid (boiling point 85-86°C, pressure 150 mmHg). The product was characterized by infrared spectroscopy (IR, thin-film method) and the main absorption peaks were: 3132, 2934, 1611, 1455, 1414, 1258, 1011, 886, 795 cm-1. The data of nuclear magnetic resonance hydrogen spectroscopy (1H NMR, CDCl3, 400 MHz) were as follows: δ 5.82 (1H, single peak, H-4), 2.36 (3H, single peak , C=CCH3), 2.23 (3H, single peak, N=CCH3). The nuclear magnetic resonance carbon spectrum (13C NMR, CDCl3) data were as follows: δ 11.3, 12.1, 102.3, 159.9, 169.1.
