L-Proline (1.81 g, 15.6 mmol) was added to a stirring, heterogeneous mixture of 4-(1H-1,2,4-triazol-1-yl)benzaldehyde (13.5 g, 78.0 mmol, Intermediate 82: step a) and 2,2-dimethyl-1,3-dioxane-4,6-dione (11.2 g, 78.0 mmol) in ethanol (520 mL) at 23° C. After 1.5 hours, diethyl 1,4-dihydro-2,6-dimethyl-3,5-pyridinedicarboxylate (19.7 g, 78.0 mmol) was added in one portion. After 16 hours, the ethanol was removed by rotary evaporation at 35° C. to afford a yellow solid. Isopropanol (300 mL) was added and the heterogeneous mixture was stirred for 10 minutes at 23° C. The mixture was filtered and the filter cake was washed with isopropanol (150 mL). The solids were collected and dried under vacuum to provide the titled compound as a white solid.
