1H, 13C, 17O NMR and quantum‐chemical study of the stereochemistry of the sulfoxide and sulfone derivatives of 3‐arylidene‐1‐thioflavan‐4‐one epoxides

Abstract

AbstractThe oxidation of the trans,cis‐(2) and trans,trans‐epoxides (3) of differently substituted (Z)‐3‐arylidene‐1‐thioflavan‐4‐ones (1) with dimethyldioxirane (DMD) yielded the appropriate sulfoxides (4, 5) and sulfones (6, 7). The structures were elucidated by the extensive application of one‐ and two‐dimensional 1H, 13C and 17O NMR spectroscopy. The conformational analysis was achieved by the application of 3J(C,H) coupling constants, NOESY responses and ab initio calculations. The preferred ground‐state conformers (twisted envelope‐A, twisted envelope‐B for 6 and twisted envelope‐A, envelope‐B for 7) were obtained as global minima of the theoretical ab initio MO study and also the examination of the 17O and 13C chemical shifts, calculated for the global minima structures of the sulfone isomers by the GIAO method. Analogous results, obtained for the sulfoxide isomers (4, 5), not only led to the preferred conformers but also gave evidence for the trans arrangement of the 2‐Ph group and the oxygen atom of the SO group. Chemical shift differences between the isomers, sulfoxides and sulfones were corroborated by ab initio calculations of the anisotropic effects of the oxirane ring and the SO and SO2 groups. Copyright © 2003 John Wiley & Sons, Ltd.