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To a solution of 1.0 M potassium tert-butoxide in tetrahydrofuran (30.7 mL, 0.0307 mol) at 0° C. was added dropwise a solution of diethyl cyanomethylphosphonate (5.20 mL, 0.0322 mol) in tetrahydrofuran (39.12 mL). The reaction was warmed to room temperature and then cooled at 0° C. again. To the reaction mixture was added a solution of tert-butyl 3-oxoazetidine-1-carboxylate (5.0 g, 0.029 mol, Aldrich: Cat. #696315) in tetrahydrofuran (7.82 mL). The reaction was allowed to warm to room temperature and stirred overnight. After quenched with water, the mixture was extracted with ethyl acetate. The combined organic layers were washed with brine, dried over MgSO4 and evaporated under reduced pressure. The crude mixture was purified by flash chromatography on a silica gel column with ethyl acetate in hexanes (0-70%) to give the desired product (5.40 g, 95%). LCMS (M+Na)+: m/z=217.1.

1. temperaturecooled at 0° C. again
2. temperatureto warm to room temperature
3. customAfter quenched with water
4. extractionthe mixture was extracted with ethyl acetate
5. washThe combined organic layers were washed with brine
6. dry with materialdried over MgSO4
7. customevaporated under reduced pressure
8. customThe crude mixture was purified by flash chromatography on a silica gel column with ethyl acetate in hexanes (0-70%)