3-(4-Cyclohexylphenyl)-3-oxo-propionic acid ethyl ester 50.25 g (0.183 moles), 4′-aminoacetanilide 25 g (0.167 moles), 4′-aminoacetanilide hydrochloride salt, 1.55 g (0.008 moles), and 500 mL of dry n-butanol were placed in a 1 liter single neck round bottom flask equipped with a Soxhlet extractor apparatus with condenser, magnetic stirrer and nitrogen inlet. In the Soxhlet thimble (33×118 mm) was placed highly activated 4A sieves (1.7-2.4 mm beads). The sieves were activated immediately before use under high vacuum with heating (400° C. for 30 min). The mixture was then brought to reflux such that the butanol azeotropically removed water, so as to drive the equilibrium reaction, and the water was removed from the butanol by the sieves before being returned to the reaction pot. The reaction was allowed to continue for 48 hrs. The charge of sieves was replaced after the first 24 hrs. Transesterification to the butyl ester along with removal of ethanol occurred concomitantly with enamine formation. After 48 hrs the reaction pot was cooled, placed in a −40° C. freezer and crystals were-allowed to form for 24 hrs. Crystals were collected by vacuum filtration and solids washed with cold ethanol. The product was then dried in a vacuum oven to give 73.8 g (98%) of the desired enamine.
