The determination of sulfoxide configuration in five-membered rings using NMR spectroscopy and DFT calculations

Cyclic five-membered ring sulfoxides and sulfones were prepared by a stepwise in situ oxidation of the corresponding sulfides with meta-chloroperbenzoic acid in an NMR tube. The oxidation was followed by NMR and both H-1 and C-13 NMR data were collected. The geometries of all of the compounds were optimized using the DFT B3LYP/6-31G** method and the C-13 and H-1 chemical shifts were calculated for geometry-optimized structures with the OFT B3LYP/6-31++G** method. The calculated C-13 chemical shifts induced by oxidation (Delta delta values) were in very good agreement with the experimental data and could be used to determine the oxidation state of the sulfur atom (-S-, -SO-, -SO2-). The characteristic differences of the induced oxidation chemical shifts of the carbon atoms in the alpha-position and beta-position to sulfur were successfully used to distinguish between the diastereoisomeric sulfoxides and allowed configuration determination. (C) 2011 Elsevier Ltd. All rights reserved.