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)piperidi ne (6). The diastereoisomers are separated by column chromatography an d the reactions of the carbanion 8a with electrophiles are studied. Se micyclic dithioacetals 12-15 are converted into the corresponding carb onyl compounds with [bis(trifluoroacetoxy)iodo]benzene (PIFA). Phenyl dichlorophosphate (PDCP) in the presence of sodium iodide and DMF is f ound to be a reagent for selective cleavage of the exocyclic C-S bond. By using DOWEX 50W and paraformaldehyde in acetone/water a cleavage o f both acetalic C-S bonds is achieved in certain cases. Copyright (C) 1996 Elsevier Science Ltd