Potassium Carbonate → tert-butyl octahydro-1H-pyrido[3,4-b][1,4]oxazine-1-carboxylate

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Reaction Steps

To a solution of trans-tert-butyl 6-(trifluoroacetyl)octahydro-1H-pyrido[3,4-b][1,4]oxazine-1-carboxylate (70 g, 0.20 mol) in MeOH (160 mL) and water (600 mL) was added K2CO3 (34.2 g, 0.24 mol) in one portion at room temperature. The mixture was stirred for 2 h at room temperature, and then extracted with DCM (200 mL×5). The combined organic layers were concentrated to give tert-butyl octahydro-1H-pyrido[3,4-b][1,4]oxazine-1-carboxylate as a mixture of trans diastereomers. SFC purification afforded the pure S,S diastereomer tert-butyl (4aS,8aS)-octahydro-1H-pyrido[3,4-b][1,4]oxazine-1-carboxylate (peak 1) 1H NMR: (CDCl3) δ 3.88-3.80 (m, 2H), 3.77-3.67 (m, 1H), 3.35-3.34 (m, 2H), 3.29-3.27 (m, 2H), 3.10-3.11 (d, 1H), 2.54-2.42 (m, 3H), 1.76 (s, 1H), 1.70-1.60 (m, 1H), 1.45 (s, 9H) LCMS (M+H)=243 and R,R diastereomer tert-butyl (4aR,8aR)-octahydro-1H-pyrido[3,4-b][1,4]oxazine-1-carboxylate (peak 2)1H NMR: (CDCl3) δ 3.89-3.80 (m, 2H), 3.77-3.67 (m, 1H), 3.35-3.34 (m, 2H), 3.29-3.27 (m, 2H), 3.10-3.11 (d, 1H), 2.54-2.42 (m, 3H), 1.76 (s, 1H), 1.70-1.60 (m, 1H), 1.44 (s, 9H) LCMS (M+H)=243.

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