[Br:1][C:2]1[CH:3]=[CH:4][C:5]([CH2:19][CH3:20])=[C:6]([CH:18]=1)[CH:7]=[C:8]1[C:12]([CH3:14])([CH3:13])[O:11][C:10]([CH3:16])([CH3:15])[C:9]1=[O:17].[OH:21]O.[OH-].[Li+]>CO>[Br:1][C:2]1[CH:3]=[CH:4][C:5]([CH2:19][CH3:20])=[C:6]([CH:7]2[C:8]3([C:9](=[O:17])[C:10]([CH3:15])([CH3:16])[O:11][C:12]3([CH3:13])[CH3:14])[O:21]2)[CH:18]=1To a solution of 4-(5-bromo-2-ethylbenzylidene)-2,2,5,5-tetramethyldihydrofuran-3-one (32.07 g, 95.15 mmol) in methanol (1570 ml) at 35° C. is added 50% aqueous hydrogen peroxide (8.10 ml, 142.73 mmol), followed immediately by a solution of 2M aqueous lithium hydroxide (9.51 ml, 19.03 mmol). This reaction mixture is stirred at 35° C. for exactly 1 hour, then quenched with saturated sodium metabisulfite (340 ml) and distilled water (340 ml). After stirring at room temperature for 15 minutes solvents are then concentrated in vacuo (to approximately 500 ml), over which time the product precipitates as a yellow solid. To this suspension is added distilled water (500 ml), and the product is isolated by filtration. After additional washing with distilled water the solid is dried under vacuum overnight to afford 2-(5-bromo-2-ethylphenyl)-4,4,6,6-tetramethyl-1,5-dioxaspiro[2.4]heptan-7-one (29.30 g) as a yellow solid which is used without purification in the next step.
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