Cesium carbonate → ethyl (7R,8S)-8-((S)-3-benzyloxycarbonylamino-2-oxo-pyrrolidin-1-yl)-1,4-dioxa-spiro[4.5]decane-7-carboxylate

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Reaction Steps

Example 1, Alternative Step 9c: Cs2CO3 (61.5 g, 0.19M, 1.5 eq) was placed in an round bottom flask and anhydrous DMSO (2.4 L) was added. Sulfonium salt 3 (80.0 g, 0.13M, 1.0 eq) was then added portionwise. Once the addition was complete the reaction mass was left to stir in the dark for 20 h. The reaction mass was then split in half and each half worked up separately: the reaction mass was diluted with EtOAc (2.0 L) and washed with brine (2 L), the organic phase was washed with brine (500 mL). The combined aq. layers were then washed EtOAc (500 mL). The combined organic phases were then washed with brine (3×750 mL). The second half of the reaction mass was treated in an identical manner and the combined organics dried over MgSO4 and concentrated to give ethyl (7R,8S)-8-{(3S)-3-Benzyloxycarbonylamino-2-oxo-pyrrolidin-1-yl}-1,4-dioxa-spiro[4.5]decane-7-carboxylate 4 as a light colored oil (56.5 g, 0.13M, ˜100 area-% purity) pure by NMR analysis. 1H-NMR: (300 MHz, CDCl3) δ 7.38-7.30 (m, 5H), 5.37 (br d, J 4.0 Hz, 1H), 5.11 (s, 2H), 4.27-4.18 (m, 1H), 4.17-3.82 (m, 8H), 3.32 (td, J 10.0Hz, 60.0 Hz, 1H), 3.23 (q, J 5.0 Hz, 1H), 2.63-2.57 (m, 1H), 2.42-2.25 (m, 2H), 1.94-1.68 (m, 5H), 1.25 (t, J 7.0 Hz, 3H). HPLC: YMC-Pack Pro C18 5 μm 4.6×150 mm, 0.05% TFA (20% MeOH, 80% H2O), to 0.05% TFA (20% MeOH, 80% MeCN), 0-100% 10 min gradient. 8.99 min (Compound 5, produced on column, 4.2 AP), 9.48 (Compound 4, 74.3 AP). HRMS: m/z 447.2127 [Calc: C23H31N2O7 447.2131].

Provenance & Evidence