Pivalaldehyde → (2S,5R)-2-tert-butyl-3-(3,5-dichloro-4-fluoro-phenyl)-5-methyl-imidazolidin-4-one

Participants

Reaction Conditions

Reaction Steps

To a solution of (R)-2-amino-N-(3,5-dichloro-4-fluoro-phenyl)-propionamide (149.1 g crude, max 594 mmol) in toluene (743 mL) at 40° C., was added pivalaldehyde (67.1 mL, 618 mmol) in one portion. The reaction was stirred at 50° C. for 22 h and then all volatiles were removed in vacuo to give a viscous brown oil. Hexane (500 mL) was added and the resulting suspension was stirred at room temperature for 30 min. The mixture was filtered and the solids rinsed with cold hexane. The filtrate was concentrated in vacuo and reprocessed in a similar manner to obtain additional precipitate. The remaining filtrate was diluted with hexane until a black oil separated from the solution. The hexane layer was decanted from this black oil and concentrated in vacuo. The residue was re-dissolved in warm diethyl ether (300 mL) and stored in the freezer for 1.5 h over which time crystal growth was observed. The solids were filtered, and the filtrate reprocessed in a similar manner to obtain additional crystals. All of the collected solids were combined to give 112.2 g of (2S,5R)-2-tert-butyl-3-(3,5-dichloro-4-fluoro-phenyl)-5-methyl-imidazolidin-4-one as a tan solid. To a solution of this solid in toluene (639 mL) at 0° C. was added triethylamine (73.5 mL, 527 mmol) in one portion. Trifluoroacetic anhydride (58.6 mL, 422 mmol) was added to the reaction mixture over 1 h at a rate to keep the internal temperature below 5° C. The reaction mixture was stirred at 0° C. for 1 h and then warmed to 20° C. over 1 h. The mixture was then cooled to 10° C. and water (1.2 L) was added. The layers were separated and the organic layer was washed with water (1.2 L and then 0.6 L). The combined aqueous layers were extracted with toluene (0.6 L). The combined organic layers were dried over MgSO4 and concentrated in vacuo to give 149.4 g of the title compound as a tan solid, m/z 456.4 [M+MeCN+H]+.

Provenance & Evidence