N-Fluorobenzenesulfonimide → Tert-butyl 8-fluoro-2-methyl-6-(trifluoromethyl)spiro[3,4-dihydropyrrolo[1,2-a]pyrazine-1,4'-piperidine]-1'-carboxylate

Participants

Reaction Steps

A solution of tert-butyl 8-bromo-2-methyl-6-(trifluoromethyl)spiro[3,4-dihydropyrrolo[1,2-a]pyrazine-1,4′-piperidine]-1′-carboxylate (15.0 g, 33.2 mmol) in THF (200 mL) was purged with Argon for 5 min. The mixture was cooled to −78° C. before nBuLi (42.5 mL of 1.6 M, 68 mmol) was added dropwise. The mixture was stirred at −78° C. for 30 min before a solution of N-(benzenesulfonyl)-N-fluoro-benzenesulfonamide (20.9 g, 66.3 mmol) in THF (100 mL) was added dropwise. The mixture was allowed to warm to room temperature overnight. The reaction mixture was quenched with sat. aq. NH4Cl. The layers were separated and the aqueous layer was extracted with EtOAc (2×). The organic layers were combined and washed with brine, dried over MgSO4, filtered and concentrated to dryness. CH2Cl2 was added and the solid was removed via filtration. The filtrate was concentrated to dryness and the residue was purified by column chromatography (10-20% EtOAc-Hex) to provide tert-butyl 8-fluoro-2-methyl-6-(trifluoromethyl)spiro[3,4-dihydropyrrolo[1,2-a]pyrazine-1,4′-piperidine]-1′-carboxylate (5.52 g, 43%) as a light brown oil that solidified upon standing. ESI-MS m/z calc. 391.4, found 392.5 (M+1)+; Retention time: 1.35 minutes (3 minute run).

Provenance & Evidence