8-Unsubstituted-3-oxo-1-thia-4, 8-diazaspiro [4, 5] decane derivatives (V) were prepared from the corresponding 8-alkoxycarbonyl derivatives (IIb, c) by the Method A (HBr-AcOH), method B
1 (KOH-iso-PrOH), or method B
2 (Claisen's alkali). V were also prepared by the reaction of 4-piperidone hydrochloride (VIII) with corresponding mercapto acids and primary amines (method C). Sulfoxides (VI) of V were prepared by method A or method D
1 (oxidation of V with H
2O
2), and sulfones (VII) were prepared by method A or method D
2 (oxidation of V with KMnO
4). VI and VII were not obtained by the method B
1 or B
2. 4-Oxo-1-thia-5, 9-diazaspiro [5, 5] undecane (V-35) was prepared by method A or method C, and the sulfone (VII-25) of V-35 was prepared by method A.
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