Picolinic acid → (S,S)-DACH-pyridyl Trost ligand

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A 22 L flask was charged with 1,1′-carbonyldimidazole (1.7 Kg, 10.48 mol) and THF (7.5 L). Solid picolinic acid (1.36 Kg, 11 mol) was added to the slurry at room temperature. The reaction was endothermic causing the mixture to cool from 18° C. to 12° C. The reaction mixture was then warmed to 18-19° C. The resulting clear solution was stirred for 1 h and molten (1S,2S)-(+)-1,2-diaminocyclohexane (0.5 Kg, 4.38 mol) was added while keeping the temperature below 50° C. The beaker and funnel were rinsed with 2.5 L of THF. The reaction was stirred at rt for 15 h. Water (0.5 L) was added to the thin slurry giving a clear solution and the reaction mixture was stirred for 1 h. The reaction mixture was concentrated to an orange semi-solid by rotary evaporation. The reaction product was slurried in 5 L of ethanol and concentrated by rotary evaporation. The reaction product was dissolved in ethanol (5 L) at 64-65° C. The solution was allowed to cool. The solution turned hazy around 58° C. At this temperature, the hazy solution was seeded (10 g) and cooled to −8° C. The resulting white crystals were isolated by filtration on a sintered glass funnel, washed with 5 L of cold ethanol (−8 to −10° C.), dried under house vacuum with nitrogen sweep, and then dried in a vacuum oven (35° C.). This resulted in the isolation of 1.23 Kg (86.3%) of white crystalline solid.

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