Diisobutylaluminum hydride → 2,3-Dihydro-1,4-benzodioxin-2-ol

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Reaction Conditions

Reaction Steps

The mixture is warmed at room temperature, then heated to reflux for 2 hours. The organic phase is washed with water, 5% aqueous sodium hydroxyde and then with water. After drying on Na2SO4, the solvent is evaporated to dryness under vacuum and the crude material is crytallized from cyclohexane-Et2O to give 1,4-benzodioxan-2-one (10 g) m.p. 52°-54° C. A molar solution of DIBAH in toluene (73 ml) is added dropwise to a stirred solution of 1,4-benzodioxan-2-one (8.9 g) in dry toluene (100 ml), cooled at -70° C. during 40 minutes. Stirring at this temperature is continued for 15 minutes, then the excess reagent is destroyed by adding 2N-isopropanol in toluene (75 ml), under stirring, at -70°÷-60° C. The mixture is warmed at room temperature and treated with 30% NaH2PO4 aqueous solution (6 ml) and 25 g of anhydrous Na 2 SO4, for 4 hours, under stirring. The inorganic material is filtered out and the eluate is evaporated to dryness to give 8.2 g of 2-hydroxy-1,4-benzodioxan. A stirred solution of this δ-lactol (7.8 g) in ethanol (30 ml) is treated with a solution of cysteamine hydrochloride (7.36 g) and potassium acetate (6.5 g) in water (12 ml). Stirring is continued for 45 minutes, then a crystalline precipitate of 2-[(o-hydroxyphenoxy)methyl]thiazolidine (8.1 g) is obtained. M.p. 76°-78° C.

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