Cl.[C:2](=[NH:10])([O:7][CH2:8][CH3:9])[CH2:3][CH2:4][CH2:5][CH3:6].[C:11]([O:15][CH2:16][CH3:17])(=[O:14])[NH:12]N.C(Cl)Cl.CO>C(O)C>[C:11]([NH:12][N:10]=[C:2]([O:7][CH2:8][CH3:9])[CH2:3][CH2:4][CH2:5][CH3:6])([O:15][CH2:16][CH3:17])=[O:14]To a solution of 7.0 g (25.3 mmole) of ethyl valerimidate hydrochloride [prepared by method of A. J. Hill and I. Rabinowitz, J. Am. Chem. Soc., 48, 734 (1926)] in 35 ml of dry ethanol stirred under N2 at -78° C. was added dropwise a solution of 24 g (23 mmole) of ethyl carbazate in 35 ml of dry ethanol. Precipitation occurred during the addition, which took 20 minutes and was accompanied by a rise in the internal temperature to -50° C. The mixture was allowed to stand at 5° C. for 60 hours and then filtered. The filtrate was concentrated, and the residue was flash chromatographed on a silica gel column (elution with 98.5:1.5 CH2Cl2 --MeOH), yielding a clear oil, homogeneous by TLC in 97:3 CH2Cl2 --MeOH; mass spectrum (FAB) m/e 217 (M+1)+. NMR suggested a mixture of syn and anti isomers.
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