[CH2:1]([N:8]([C:17]([NH:19][CH2:20][CH3:21])=[O:18])[NH:9]C(OC(C)(C)C)=O)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C(=O)(O)[O-].[Na+]>FC(F)(F)C(O)=O.ClCCl>[CH2:1]([N:8]([C:17]([NH:19][CH2:20][CH3:21])=[O:18])[NH2:9])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1A solution of of 2-benzyl-1-tert-butoxycarbonyl-4-ethylsemicarbazide (2.8 g, 9.6 mmol) in 50% trifluoroacetic acid in dichloromethane (10 ml) was stirred for 10 min at room temperature. Then saturated sodium bicarbonate was added until pH>7 and the aqueous layer was extracted with dichloromethane (2×10 ml) and the combined organic layers were dried (magnesium sulfate) and concentrated in vacuo. The obtained oil was chromatographed on silica (100 g) with ethyl acetate as eluent to give 1.7 g of 2-benzyl-4-ethylsemicarbazide.
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