C,C-coupling with sulfur-stabilized carbanions .6. Preparation and electrophilic substitution of 1-[3-methyl-2-(2-thiolanylthio)butyl]piperidine and dethioacetalization of semicyclic dithioacetals

1-[3-Methyl-2-(2-thiolanylthio)butyl]piperidine (8) is obtained from L-valine via enantiomerically pure 1-(2-mercapto-3-methylbutyl)piperidine (6). The diastereoisomers are separated by column chromatography and the reactions of the carbanion 8a with electrophiles are studied. Semicyclic dithioacetals 12-15 are converted into the corresponding carbonyl compounds with [bis(trifluoroacetoxy)iodo]benzene (PIFA). Phenyl dichlorophosphate (PDCP) in the presence of sodium iodide and DMF is found to be a reagent for selective cleavage of the exocyclic C-S bond. By using DOWEX 50W and paraformaldehyde in acetone/water a cleavage of both acetalic C-S bonds is achieved in certain cases. Copyright (C) 1996 Elsevier Science Ltd