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0 °C

Dimethyl D-glutamate hydrochloride (2.1 g, 10.00 mmol) was dissolved in methanol (7.5 ml) and tetrahydrofuran (15 ml) and the mixture was then treated with crushed sodium hydroxide (0.402 g, 10.05 mmol) for 20 minutes under argon. At this stage acetic acid (0.575 ml, 10.05 mmol) and cyclopentanone (0.889 ml, 10.05 mmol) were added to the mixture. After stirring for 10-15 minutes the mixture was cooled to 0° C. in an ice-bath and treated with sodium borohydride pellets (0.380 g, 10.05 mmol). The mixture was stirred for 3 hrs under argon and allowed to warm to room temperature. Once the mixture had reached room temperature the methanol was evaporated off and the residue was diluted with dichloromethane (20 ml) and washed with saturated aqueous sodium hydrogen carbonate (˜25 ml). The organic layer was separated and the aqueous layer was back-extracted with more dichloromethane (2×20 ml). The combined organic layers were concentrated in vacuo to give an oil. The oil was dissolved in toluene (10 ml) and heated at reflux overnight. The solvent was then evaporated and the resulting residue was purified by flash-silica column chromatography, eluting with a gradient of 0-10% methanol in dichloromethane, to give crude methyl 1-cyclopentyl-5-oxoprolinate which was used without further purification in the next step.

1. stirringThe mixture was stirred for 3 hrs under argon
2. temperatureto warm to room temperature
3. customhad reached room temperature
4. customwas evaporated off
5. additionthe residue was diluted with dichloromethane (20 ml)
6. washwashed with saturated aqueous sodium hydrogen carbonate (˜25 ml)
7. customThe organic layer was separated
8. extractionthe aqueous layer was back-extracted with more dichloromethane (2×20 ml)
9. concentrationThe combined organic layers were concentrated in vacuo
10. customto give an oil
11. temperatureheated
12. temperatureat reflux overnight
13. customThe solvent was then evaporated
14. customthe resulting residue was purified by flash-silica column chromatography
15. washeluting with a gradient of 0-10% methanol in dichloromethane