Step 1: (DADC) 2 mg of the complex (1 equiv) was dissolved in dry pyridine (20% solution) and cooled in an external ice/water bath under N2. The corresponding acid chloride 3 (4.4 equiv) was added at 0-5 C and stirred at room temperature for 1-2 days. After ice/HCl (2N) hydrolysis, the mixture was repeatedly extracted with CH2Cl2. The bound organic layer was washed with satd. NaHCO3 solution, dried (Na2SO4), decolorized (charcoal), filtered and concentrated. Conversion of 1.00 g 1 (2.34 mmol) with acetyl chloride according to method B and chromatographic purification gave 0.58 g (46%) of 4a.13C NMR (50 MHz, CDCl3):= 14.0 (q), 18.4 (q), 61.7 (t), 121.6, 164.0, 165.2, 171.7 ppm.
Step 2: The diester was dissolved in a 5/1 mixture of 2N HCl and acetic acid (5%) and refluxed for 5-30 hours until TLC showed complete conversion. The reaction was hydrolyzed with satd. NaHCO3 solution and extracted with CH2Cl2. The bound organic layer was dried (Na2SO4), filtered and evaporated to give 5 without further purification. Colorless crystals of 2,6-dimethyl-4-pyrone 0.50 g (1.86 mmol) were obtained (87% yield).
