N-Fluorobenzenesulfonimide → 10-Fluoro-3,4,6,7,8,9-hexahydropyrazino[1,2-a]indol-1(2H)-one

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Reaction Conditions

Reaction Steps

Into a 2-L 4-necked round-bottom flask purged and maintained with an inert atmosphere of nitrogen was placed a solution of 119a (40 g, 148.62 mmol, 1.00 equiv) in tetrahydrofuran (200 mL), followed by the addition of n-BuLi (2.4 M) (218 mL, 3.50 equiv) dropwise with stirring at −78° C. The resulting solution was stirred at −40° C. for 3 h. To this was added a solution of N-fluorobenzenesulfonimide (98.7 g, 313.33 mmol, 2.10 equiv) in tetrahydrofuran (200 mL) dropwise with stirring at −78° C. The resulting solution was stirred at room temperature for 3 h, quenched by the addition of 200 mL of water and extracted with 3×500 mL of ethyl acetate. The combined organic layers were dried over anhydrous sodium sulfate and concentrated under vacuum. The crude product (30 g) was purified by Prep-HPLC with the following conditions (mobile phase, A: 0.05% trifluoroacetic acid/water; B: CH3CN; gradient: 10% B-25% B) to afford 5.05 g (16%) of 119b as a white solid. MS: [M+H]+ 209. 1H NMR (300 MHz, CDCl3) δ 6.16 (br, 1H), 3.90-3.86 (m, 2H), 3.65-3.62 (m, 2H), 2.53-2.47 (m, 4H), 1.88-1.80 (m, 2H), 1.77-1.72 (m, 2H).

Provenance & Evidence