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A solution of 4-hydroxy-3-isobutyryl-6-isopropyl-pyran-2-one (10.26 g, 45.8 mmol) in conc. H2SO4 (40 mL) is stirred at 130° C. for 15 min. The dark reaction mixture is then cooled to 0° C., and crushed ice (˜200 g) is added with stirring. The resulting solution is extracted thrice with Et2O, and the combined extracts are dried over Na2SO4 and concentrated. The crude material is purified by flash chromatography on silica gel. Gradient elution with 3:2 hexanes-EtOAc, 1:1 EtOAc-hexanes, 2:1 EtOAc-hexanes, and 3:1 EtOAc-hexanes affords 4-hydroxy-6-isopropyl-pyran-2-one as a light yellow solid. 1H NMR (CDCl3, 300 MHz) δ 11.2 (br, 1H), 6.00 (d, J=1.8 Hz, 1H), 5.58 (d, J=1.8 Hz, 1H), 2.73 (sept, J=6.9 Hz, 1H), 1.22 (d, J=6.9 Hz, 1H) ppm.

1. customThe dark reaction mixture
2. additionis added
3. extractionThe resulting solution is extracted thrice with Et2O
4. dry with materialthe combined extracts are dried over Na2SO4
5. concentrationconcentrated
6. customThe crude material is purified by flash chromatography on silica gel
7. washGradient elution with 3:2 hexanes-EtOAc, 1:1 EtOAc-hexanes, 2:1 EtOAc-hexanes, and 3:1 EtOAc-hexanes