A13C nuclear magnetic resonance study of thiolane sulfoxides. The configurations of neothiobinupharidine sulfoxides

The sulfoxide configurations of neothiobinupharidine α- and β-sulfoxides have been determined through a 13C nmr investigation. The 13C nmr sulfoxidation increments (ΔδC-i = δC–iS–O − δC–iS) for all carbons in 2,2,4,4-tetramethylthiolane sulfoxide have been determined, Sulfoxidation increments for the C-2 methyl groups, the indicator carbons, were found to be similar in sign and magnitude to the increments reported for methyl groups in penicillin sulfoxides, wherein methyl groups cis to the sulfoxide oxygen show larger sulfoxidation increments than do the trans methyl groups. The sign and magnitude of the sulfoxidation increments for C-6 and C-8, the indicator carbons in the neothiobinupharidine sulfoxides, have been determined and compared with those of the model 2,2,4,4-tetramethylthiolane and those of the penicillins. The C-6 increments were −9.9 and −5.6 ppm respectively for the solid and liquid neothiobinupharidine sulfoxide. Therefore the solid sulfoxide is assigned the β-configuration and the liquid sulfoxide the α-configuration as a result of these studies.