Tetrahydrofuran → Ethyl N-boc-L-proline-4-ene

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Reaction Steps

At −50° C. a solution of lithium triethylborohydride in THF (1.0 M, 107 mL, 1.07 eq) is added dropwise to a solution of (S)-5-oxo-pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester 2-ethyl ester (100 mmol, 1.0 eq) in toluene (170 mL). After 45 min DIPEA (450 mmol, 4.5 eq) and powdered DMAP (1.31 mmol) are added slowly at −50° C. The mixture is treated with trifluoroacetic anhydride (120 mmol, 1.20 eq) while keeping the internal temperature below −45° C., allowed to reach RT within 90 min and stirred for additional 17 h. At 0° C. water (250 mL) is added slowly and the layers are separated. The organic layer is washed with ice-cold water (3×250 mL) and concentrated in vacuo to give the desired product as an orange liquid. LC-MS (acidic): tR=0.93 min; [M+H]+=242.2.

Provenance & Evidence