Sulfuric Acid → 3,4-dihydro-2H-1-benzopyran-2-carboxylic acid

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Reaction Steps

6,8-di-t-Butyl-2-hydroxycarbonylchroman (2.90 g, 0.01 mol) obtained in Example 3 was dissolved in toluene (27 g), and the resulting solution was added dropwise to a suspension of aluminum chloride (2.67 g, 0.02 mol) in toluene at room temperature. After the dropwise addition, the mixture was stirred at room temperature for 2 h. The reaction mixture was poured into aqueous sulfuric acid solution and the organic layer was separated. An aqueous alkaline solution was added to the organic layer and the aqueous layer was separated. An aqueous sulfuric acid solution was added to the aqueous layer and the mixture was extracted with toluene. The extract was concentrated under reduced pressure. The residue was quantitatively analyzed by liquid chromatography according to the internal standard method. As a result, 2-chroman-carboxylic acid was obtained in a yield of 90% [net 1.60 g, 0.009 mol]. The 1H-NMR data of the obtained 2-chroman-carboxylic acid are shown below.

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