p-Toluenesulfonic acid monohydrate → tert-Butyl 2'-methyl-3',4'-dihydro-2'H-spiro[piperidine-4,1'-pyrrolo[1,2-a]pyrazine]-1-carboxylate

Participants

Reaction Conditions

Reaction Steps

N-Methyl-2-pyrrol-1-yl-ethanamine (2.19 g, 17.64 mmol), tert-butyl 4-oxopiperidine-1-carboxylate (3.51 g, 17.64 mmol), and pTsOH.H2O (0.334 g, 1.76 mmol) were combined in ethanol (87.60 mL) and heated at 70° C. for 4 h. The reaction was concentrated and the residue was dissolved in dichloromethane. The organics were washed with a saturated NaHCO3 solution and brine. The organics were dried over sodium sulfate and evaporated. The crude material was purified by silica gel chromatography eluting with 0-10% methanol in dichloromethane with 2% triethylamine to give tert-butyl 2-methylspiro[3,4-dihydropyrrolo[1,2-a]pyrazine-1,4′-piperidine]-1′-carboxylate (4.2 g, 78%). ESI-MS m/z calc. 305.4, found 306.3 (M+1)+; Retention time: 0.97 minutes (3 min run). 1H NMR (400 MHz, CDCl3) δ 6.55-6.52 (m, 1H), 6.15-6.11 (m, 1H), 5.92-5.89 (m, 1H), 3.92 (t, J=6.0 Hz, 2H), 3.91-3.75 (m, 2H), 3.29 (t, J=6.0 Hz, 2H), 3.26-3.12 (m, 2H), 2.36 (s, 3H), 2.10-1.99 (m, 2H), 1.83-1.69 (m, 2H), 1.47 (s, 9H).

Provenance & Evidence