Dicyclohexylcarbodiimide → N,N'-Dicyclohexylurea

Participants

Reaction Conditions

Reaction Steps

Dicyclohexylcarbodiimide (6.81 g) is added to a solution, cooled to 5° C., of N-t-butoxycarbonyl-L-serine (6.16 g) and t-butyl glycinate (3.93 g) in methylene chloride (100 cc). The reaction mixture is stirred for 30 minutes at 5° C. and then for 18 hours at about 20° C. The precipitate of dicyclohexylurea formed is filtered off and washed twice with methylene chloride (40 cc in total). The combined organic phases are washed successively 3 times with a saturated solution of sodium bicarbonate (90 cc in total) and twice with water (60 cc in total), dried over sodium sulphate and concentrated to dryness under reduced pressure (20 mm Hg; 2.7 kPa) at 20° C. This yields an oil (10.22 g) which is chromatographed on neutral silica gel (0.04-0.063 mm) (100 g) contained in a column of diameter 3.4 cm. Elution is carried out successively with a cyclohexane/ethyl acetate mixture (1/1 by volume) (500 cc) and a cyclohexane/ethyl acetate mixture (1/3 by volume) (600 cc), 100 cc fractions being collected. Fractions 5 to 8 are combined and concentrated to dryness under reduced pressure (20 mm Hg; 2.7 kPa) at 50° C. This yields t-butyl N-t-butoxycarbonyl-L-seryl-glycinate (2.64 g) in the form of an oil which crystallises slowly.

Provenance & Evidence