1 ethylpropoxy 1 cyclohexene 1 carboxylate were added under stirring after fast addition 10 15 min of two thirds ca 160 ml of the total volume of this solution the addition was stopped and the supersaturated clear solution was seeded with 0 2 g of previously obtained ethyl 3r 4r 5s 4 acetamido 5 amino 3 1 ethylpropoxy 1 cyclohexene 1 carboxylate phosphate 1 1 immediately afterwards crystallization commenced the resulting thick suspension was stirred for 45 60 min at 50 55 u00b0 c then the remaining amine solution was slowly added 45 60 min to the suspension at 50 55 u00b0 c the feeder was rinsed with 20 ml ethanol subsequently the thick suspension was continuously cooled to 12 20 u00b0 c in about 4 h cooling speed 10 u00b0 c h to complete the crystallization stirring was continued at 12 20 u00b0 c for additional 2 u00b1 1 h ethyl 3r 4r 5s 4 acetamido 5 amino 3 1 ethylpropoxy 1 cyclohexene 1 carboxylate phosphate 1 1 was isolated by pressure filtration 0 3 bar nitrogen overpressure dacron u00ae filter cloth the crystalline product was washed twice with 240 ml acetone and twice with 300 ml n heptane at room temperature ethyl 3r 4r 5s 4 acetamido 5 amino 3 1 ethylpropoxy 1 cyclohexene 1 carboxylate phosphate 1 1 was dried in vacuo u2248 20 mbar at a maximum temperature of 50 u00b0 c until constant weight yield 54 55 g 88 91 of the title product in the form of colorless needles with an assay of 99 wt sum of impurities lt 0 5 wt single impurities u2266 0 1 wt 100 g 0 295 mol ethyl 3r 4r 5s 4 acetamido 5 azido 3 1 ethylpropoxy 1 cyclohexene 1 carboxylate were dissolved.