Ammonium Chloride → 4-Hydroxy-5,5-dimethylcyclopent-2-enone

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Cerium (III) chloride heptahydrate (16.5 g, 44.3 mmol) was added to a stirred solution of the enedione 3 (5.00 g, 40.3 mmol) in methanol (150 ml) at room temperature, under an atmosphere of nitrogen. The resulting mixture was then cooled to −78° C. and sodium borohydride (1.68 g, 44.4 mmol) was added in portions over 30 minutes. The mixture was stirred at −78° C. for a further 2 hours, then at −30° C. for 45 minutes. Ammonium chloride (sat'd. aq., 150 ml) was then added and the mixture was extracted with ethyl acetate (3×150 ml). The combined organic extracts were then dried over MgSO4, and evaporated in vacuao. Flash chromatography (SiO2, 80% diethyl ether in hexane) gave the hydroxy-ketone 4 (3.58 g, 28.4 mmol, 71%) as a white solid; δH (300 MHz, CDCl3) 7.46 (1H, dd J 5.9 & 2.2 Hz, CH═CHC═O), 6.20 (1H, dd J 5.9 & 1.4 Hz, CH═CHC═O), 4.59-4.57 (1H, m, CHOH), 1.16 (3H, s, CH3), 1.07 (3H, s, CH3); δC (75.5 MHz, CDCl3) 211.7 (s), 160.6 (d), 132.7 (d), 79.8 (d), 48.2 (s), 22.7 (q), 20.0 (q).

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