Under sonication conditions, 10 g of monomethyl 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)pyridine-3,5-dicarboxylate was placed in a 200 mL reaction flask, to which 14 mL of N,N-dimethylformamide (DMF) and 56 mL of dichloromethane were added. Under ice bath conditions, 2.4 mL of thionyl chloride was slowly added to the resulting homogeneous suspension, followed by stirring the reaction mixture for 1 hour until a clarified solution was formed. Next, 6.3 g of 1-benzyl-3-piperidinol was added and stirring was continued for 2.5 hours under ice bath conditions. Upon completion of the reaction, the reaction solution was washed with 40 mL of water (repeated 4 times) and 40 mL of saturated brine solution (1 time). The organic phase was dried by adding 4 g of anhydrous sodium sulfate for 2 hours. After drying, the sodium sulfate solid was removed by filtration and the dichloromethane was recovered by distillation under reduced pressure to give the crude yellow to red (R)-rel-3-((R)-1-benzylpiperidin-3-yl)5-methyl 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate hydrochloride. The crude product was dissolved in 100 mL of acetone and sonicated at 150 W and 40 kHz for 7 min, followed by filtration under reduced pressure and drying to give 5.9 g of yellow powdery product in 36.2% yield.
