[CH3:1][C:2]1([CH3:18])[S:12][CH2:11][N:10]2[CH:3]1[CH2:4][CH:5]1[CH:9]2[CH2:8][N:7](C(OCC)=O)[CH2:6]1.C(=O)([O-])[O-].[K+].[K+]>O>[CH3:1][C:2]1([CH3:18])[S:12][CH2:11][N:10]2[CH:3]1[CH2:4][CH:5]1[CH:9]2[CH2:8][NH:7][CH2:6]16 g (22.2 mmol) of ethyl 9,9-dimethyl-10-thia-1,4-diazatricyclo[6.3.0.02,6 ]undecane-4-carboxylate together with 12 g of Ba(OH)2 ×8H2O are refluxed overnight in 100 ml of water. Potassium carbonate is added, barium carbonate is filtered off with suction, and the filtrate is extracted ten times using 100 ml portions of chloroform. The extracts are dried over potassium carbonate and concentrated, and the residue is distilled.
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