Acetic Anhydride → (5R)-4-chloro-5-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidin-7-yl acetate

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A solution of (R)-4-chloro-5-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidine 1-oxide (5.5 g, 30 mmol) in Ac2O (40 ml) was heated to 110° C. for 3 hours. After cooling, the acetic anhydride was evaporated under vacuum. The residue was taken up in DCM and added to a stirring cold solution of saturated NaHCO3 solution. The layers were extracted with DCM, dried over MgSO4, filtered, and concentrated. The crude black/dark brown oil was chromatographed (Biotage) eluting with 20% EtOAc/Hexane to give (5R)-4-chloro-5-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidin-7-yl acetate (3.0 g, 44%). 1H NMR (CDCl3, 400 MHz) δ 8.92 (m, 1H), 6.30-6.03 (m, 1H), 3.60-3.30 (m, 1H), 2.84 (m, 1H), 2.40-2.20 (m, 1H), 2.15 (d, J=6 Hz, 2H), 1.75 (m, 2H), 1.47 (d, J=6.8, 2H), 1.38 (d, J=7.2, 1H). MS (APCI+) [M+H]+227.

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