The general procedure for the synthesis of tert-butyl [4,4'-bipiperidinyl]-1-carboxylate from di-tert-butyl dicarbonate and 4,4'-bipiperidinium dihydrochloride is as follows:
1. prepare 4-(4-piperidinyl)-1-piperidine carboxylic acid, 1,1-dimethylethyl ester (LXXXIX).
2. dissolve 41 g (0.17 mol) of 4,4'-bipiperidine dihydrochloride in 250 mL of ethanol and 250 mL of 2N sodium hydroxide solution.
3. 18.5 g (0.085 mol) of tert-butyl dicarbonate was slowly added to a 100 mL ethanol solution at 0°C.
4. The reaction mixture was stirred at 10 °C for 1 hour.
5. The ethanol was removed using a rotary evaporator.
6. The residual aqueous phase was saturated with sodium chloride and extracted with ethyl acetate.
7. The organic phases were combined, dried with magnesium sulfate and concentrated under reduced pressure.
8. The crude product was purified by silica gel column chromatography, the eluent being a mixture of dichloromethane/methanol/ammonia (8:2:0.4, v/v).
9. 16.5 g of the target compound tert-butyl [4,4'-bipiperidine]-1-carboxylate was finally obtained as a white solid in 72% yield, with a melting point of 70-71°C. The product was purified by silica gel column chromatography.
