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0 °C

A round-bottom flask was charged with ethyl 2-ethyl-4-oxocyclopentanecarboxylate (95.9 g, 521 mmol) and DCE (1.8 L). The solution was cooled to about 0° C. and AcOH (45 mL, 780 mmol) and dibenzylamine (120 mL, 625 mmol) were added drop-wise, resulting in the formation of a thick suspension. The reaction mixture was warmed to about 10° C. by removing the cooling bath and additional DCE (500 mL) was added. Sodium triacetoxyborohydride (166 g, 781 mmol) was added portion-wise and the reaction mixture was stirred at room temperature for about 20 h. The reaction mixture was slowly poured into saturated aqueous NaHCO3 (1.5 L) with stirring followed by the portion-wise addition of solid NaHCO3 (175 g, 2083 mmol). The mixture was stirred for about 2 h and the organic layer was separated, dried over anhydrous Na2SO4, and concentrated to dryness under reduced pressure. The crude yellow oil was purified by flash column chromatography using EtOAc/heptane as eluant (0-20% EtOAc) to yield ethyl 4-(dibenzylamino)-2-ethylcyclopentanecarboxylate (136.6 g, 72%) as a white solid: LC/MS (Table 2, Method a) Rt=3.26 min; MS m/z: 366 (M+H)+.

1. customresulting in the formation of a thick suspension
2. temperatureThe reaction mixture was warmed to about 10° C.
3. customby removing the cooling bath and additional DCE (500 mL)
4. additionwas added
5. stirringwith stirring
6. stirringThe mixture was stirred for about 2 h
7. customthe organic layer was separated
8. dry with materialdried over anhydrous Na2SO4
9. concentrationconcentrated to dryness under reduced pressure
10. customThe crude yellow oil was purified by flash column chromatography