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To a solution of compound 51 (2.01 g, 6.923 mmol) in ethanol (50 mL) was added 10% palladium on carbon (737 mg, wet) in one portion under argon protection. The flask was evacuated and re-filled with argon three times (to remove oxygen), and the mixture stirred at room temperature overnight under one atmosphere of hydrogen. The reaction system was then purged with nitrogen, and the catalyst was vacuum filtered and washed with ethanol (2×5 mL). The filtrate and washings were combined and concentrated under reduced pressure. The residue was chromatographed over silica gel, eluting with a mixture of ethyl acetate (0–25%) and hexanes (100–75%), to afford 1.75 g (96%) of the product 52 as a colorless viscous oil. 1H NMR (CDCl3) δ 1.44 (s, 9H), 1.47–1.64 (m, 4H), 2.50 (t, J=7.1 Hz, 2H), 3.08–3.14 (m, 2H), 3.57 (br s, 2H), 4.55 (br s, 1H), 6.62 (d, J=8.2 Hz, 2H), 6.95 (d, J=8.2 Hz, 2H). m/z (APCI)=265 [C15H24N2O2+H]+.

1. customThe flask was evacuated
2. additionre-filled with argon three times (to remove oxygen)
3. customThe reaction system was then purged with nitrogen
4. filtrationfiltered
5. washwashed with ethanol (2×5 mL)
6. concentrationconcentrated under reduced pressure
7. customThe residue was chromatographed over silica gel
8. washeluting with a mixture of ethyl acetate (0–25%) and hexanes (100–75%)