[OH:1][CH:2]([CH3:10])/[CH:3]=[CH:4]/[C:5]([O:7][CH2:8][CH3:9])=[O:6].[CH:11]1([N:17]=[C:18]=[O:19])[CH2:16][CH2:15][CH2:14][CH2:13][CH2:12]1>C1(C)C=CC=CC=1>[CH:11]1([NH:17][C:18]([O:1][CH:2]([CH3:10])/[CH:3]=[CH:4]/[C:5]([O:7][CH2:8][CH3:9])=[O:6])=[O:19])[CH2:16][CH2:15][CH2:14][CH2:13][CH2:12]1Reaction of 21 (rac-Ethyl (2E)-4-hydroxypent-2-enoate) (1.44 g, 10 mmol) with cyclohexyl isocyanate (2.53 ml, 20 mmol) in toluene (8 ml) according to Example 1. Purification by flash chromatography (AcOiPr:heptane fraction 15:85 to 25:75) yields 5 (rac-Ethyl (2E)-4-(cyclohexylaminocarbonyloxy)pent-2-enoate) (2.29 g, 85%) as a yellowish solid.
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