[CH3:1][C:2]1([CH3:10])[CH2:7][C:6](=[O:8])[CH2:5][C:4](=O)[CH2:3]1.CO[CH:13](OC)[CH2:14][NH2:15].O.C1(C)C=CC(S(O)(=O)=O)=CC=1>C1(C)C=CC=CC=1>[CH3:10][C:2]1([CH3:1])[CH2:3][C:4]2[NH:15][CH:14]=[CH:13][C:5]=2[C:6](=[O:8])[CH2:7]1A solution of 5,5-dimethyl-1,3-cyclohexandione (30 g, 0.21 mol), aminoacetaldehyde dimethyl acetal (35 mL, 0.32 mol) and p-toluenesulphonic acid hydrate (1.5 g, 8 mmol) in toluene (250 mL) were heated at reflux for 4 h using Dean-Stark apparatus to remove the water. The toluene was evaporated and the residue dissolved in 3N HCl (250 mL). The solution was heated at 60° C. for 6 h. After this time the mixture was cooled to room temperature and extracted with DCM (6×). The combined organic layers were dried (MgSO4), evaporated and the residue chromatographed on silica gel, eluting with isohexane: EtOAc (4:1→1:1). The fractions containing the desired product were combined, evaporated and the residue triturated with ether. The title compound (1.8 g, 5%) was isolated as a cream solid. mp 177-178° C. 1H NMR (360 MHz, d6-DMSO) 8 1.02 (6H,s), 2.19 (2H,s), 2.63 (2H,s), 6.23 (1H,t, J=3.9 Hz), 6.71 (1H,t, J=3.9 Hz). MS (ES+) 164 (M+1).
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