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

Participants

Reaction Steps

To a solution of tert-butyl 8-bromo-2-methyl-6-(trifluoromethyl)spiro[3,4-dihydropyrrolo[1,2-a]pyrazine-1,4′-piperidine]-1′-carboxylate (5.00 g, 11.1 mmol) in anhydrous THF (125 mL) at −78° C. was added nBuLi (8.84 mL of 2.5 M, 22.1 mmol) slowly. The reaction mixture was allowed to stir at −78 for 20 minutes before 1,1,1,2,2,2-hexachloroethane (5.36 g, 22.7 mmol) was added dropwise as a solution in THF (12 mL). The reaction mixture was allowed to slowly warm to room temperature and was stirred overnight. The reaction mixture was quenched with the addition of saturated aqueous ammonium chloride (100 mL). The volatiles were removed under reduced pressure to half volume. The remaining aqueous suspension was extracted with EtOAc (2×100 mL). The combined organic layers were dried over sodium sulfate, filtered and concentrated under reduced pressure to afford a thick brown oil. The crude product was purified by silica gel column chromatography: 10-20% EtOAc/hexane gradient to provide tert-butyl 8-chloro-2-methyl-6-(trifluoromethyl)spiro[3,4-dihydropyrrolo[1,2-a]pyrazine-1,4′-piperidine]-1′-carboxylate (2.40 g, 53%) as a yellow oil that crystallized upon standing. ESI-MS m/z calc. 407.2, found 407.9 (M+1)+; Retention time: 1.70 minutes (3 min run). 1H NMR (400 MHz, CDCl3) δ 6.47 (s, 1H), 3.97 (t, J=5.5 Hz, 4H), 3.28 (s, 2H), 3.13 (s, 2H), 2.51-2.28 (m, 5H), 1.93 (d, J=13.7 Hz, 2H), 1.47 (d, J=9.5 Hz, 9H).

Provenance & Evidence