Absolute Configuration and Conformational Stability of (+)-2,5-Dimethylthiolane and (−)-2,5-Dimethylsulfolane

Enantiopure (+)-2,5-dimethylthiolane and (−)-2,5-dimethylsulfolane were prepared using literature procedures and investigated using vibrational circular dichroism (VCD). Experimental absorption and VCD spectra of (+)-2,5-dimethylthiolane and (−)-2,5-dimethylsulfolane in CCl4 solution in the 2000−900 cm-1 region were compared with the ab initio predictions of absorption and VCD spectra obtained with density functional theory using the B3LYP/6-311G(2d, 2p) basis set for different conformers of (2R,5R)-2,5-dimethylthiolane and (2R,5R)-2,5-dimethylsulfolane. This comparison indicates that (+)-2,5-dimethylthiolane is of the (2R,5R)-configuration and has two predominant conformations in CCl4 solution. In addition, (−)-2,5-dimethylsulfolane is of (2R,5R)-configuration and has only one predominant conformation. The stereochemical assignment is in agreement with literature.