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The crude (6-fluoro-2,2-dimethyl-4H-1,3-benzodioxin-8-yl)methanol (35.15 g, 166 mmol) was dissolved in biphasic mixture of CH2Cl2 (230 mL) and water (180 mL). The mixture was cooled to 0° C., and TEMPO (519 mg, 3.3 mmol) and KBr (2.0 g, 16.6 mmol) were added. Finally, NaClO (aq) (5%, 500 mL, 332 mmol) saturated with NaHCO3 was added gradually by addition funnel. The mixture was stirred for 15 min after the all the reagents were added. The layers were partitioned, and the aqueous phase was extracted with CH2Cl2. The organic extracts were combined, dried over magnesium sulfate, filtered, and concentrated in vacuo. The resulting solid was triturated sequentially with hexanes and methanol to yield a white crystalline solid. This procedure was repeated two more times on a further 38 g of (6-fluoro-2,2-dimethyl-4H-1,3-benzodioxin-8-yl)methanol (179 mmol). The triturated solids of all three experiments were combined to provide 51.1 g of 6-fluoro-2,2-dimethyl-4H-1,3-benzodioxine-8-carbaldehyde (243 mmol, 70% yield). 1H NMR (400 MHz, CDCl3): δ 10.37 (d, 1H), 7.41 (dd, 1H), 6.96-6.94 (m, 1H), 4.88 (s, 2H), 1.61 (s, 6H).

1. additionwere added
2. customThe layers were partitioned
3. extractionthe aqueous phase was extracted with CH2Cl2
4. dry with materialdried over magnesium sulfate
5. filtrationfiltered
6. concentrationconcentrated in vacuo
7. customThe resulting solid was triturated sequentially with hexanes and methanol
8. customto yield a white crystalline solid