Into a 1 liter single-neck round-bottom flask equipped with a Soxhlet extractor apparatus with condenser, magnetic stirrer and nitrogen inlet was placed 50.25 g (0.183 moles) of 3-(4-cyclohexylphenyl)-3-oxo-propionic acid ethyl ester, 25 g (0.167 moles) of 4′-aminoacetanilide, 1.55 g (0.008 moles) 4′-aminoacetanilide hydrochloride salt and 500 mL of dry n-butanol. Into the Soxhlet thimble (33×118 mm) was placed highly activated 4A sieves (1.7-2.4 mm beads). These sieves are 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, driving 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. It was necessary to replace the charge of sieves after the first 24 hrs. Transesterification to the butyl ester along with removal of ethanol occurs concomitantly with enamine formation. After 48 hrs the reaction pot was cooled, then placed in a −40° C. freezer and crystals were allowed to form over 24 hrs. The crystals were collected by vacuum filtration and the solids washed with cold ethanol. The product was then dried in a vacuum oven to give 73.8 g (98%) of the desired enamine.
