18742-02-4

82891-99-4

General procedure for the synthesis of 2-(2-bromoethyl)-1,3-dioxolane from 2-(2-bromoethyl)-1,3-dioxolane: To a solution of 2-(2-bromoethyl)-1,3-dioxolane (40.73 g, 225 mmol) in anhydrous DMSO (350 mL) was slowly added NaNO2 (27.95 g, 405 mmol) at 0 °C. ) to a solution of anhydrous DMSO (350 mL). The reaction mixture was stirred at 18 °C for 6 h under nitrogen protection. Upon completion of the reaction, the mixture was poured into water and extracted with methyl tert-butyl ether (MTBE). The organic phases were combined, washed with saturated brine, dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography to afford 2-(2-nitroethyl)-1,3-dioxolane (12.50 g, 38% yield) as a yellow liquid. Subsequently, the above intermediate (3.97 g, 27 mmol) was stirred with tert-butyl 4-formylpiperidine-1-carboxylate (6.61 g, 31 mmol) in triethylamine (TEA, 3.00 g, 30 mmol) at 18 °C for 8 hours. After addition of 4-dimethylaminopyridine (DMAP, 330 mg, 2.70 mmol) in a solution of acetic anhydride (Ac2O, 4.13 g, 40 mmol), stirring was continued at 18°C for 7 hours. The reaction was quenched with water and extracted with ethyl acetate (EtOAc). The organic phases were combined, washed with saturated brine, dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure. The residue was purified by silica gel column chromatography to afford tert-butyl 4-[(Z)-3-(1,3-dioxolan-2-yl)-2-nitro-prop-1-enyl]piperidine-1-carboxylate (5.64 g, 61% yield) as a yellow liquid. Finally, the above intermediate (2.50 g, 7.30 mmol) was dissolved in anhydrous ethanol (EtOH, 100 mL) and chloroform (CHCl3, 8 mL) containing PtO2 (414 mg, 1.83 mmol), and stirred for 15 hr at 18 °C under 50 psi hydrogen pressure. The reaction mixture was filtered through diatomaceous earth and washed with ethanol. The filtrate was concentrated to dryness to afford the target product R-04b (2.02 g, 88% crude yield) as a yellow slurry, which was used directly in the next step of the reaction.ESI-MS (M + 1): 315.3 (calculated value C16H30N2O4: 314.2).