Determination of Absolute Configuration Using Vibrational Circular Dichroism Spectroscopy: The Chiral Sulfoxide 1-Thiochroman-S-Oxide

We have determined the absolute configuration of the chiral sulfoxide 1-thiochroman S-oxide 1 using vibrational circular dichroism (VCD) spectroscopy. The VCD spectrum of a CCl4 solution of 1 was analyzed using density functional theory (DFT), which predicts three stable conformations of 1, separated by <1 kcal/mol. The VCD spectrum predicted using the DFT/GIAO methodology for the equilibrium mixture of the three conformations of (S)-1 is in excellent agreement with the experimental spectrum of (+)-1. The absolute configuration of 1 is therefore (R)-(-)/(S)-(+). (+)-1 and (-)-1 of high enantiomeric excess (e.e.) were synthesized in high yields via asymmetric oxidation of 1-thiochroman 2 using Ti(iso-PrO)4/(R,R)-1,2-diphenylethane-1,2-diol/H2O/ tert-butyl hydroperoxide and Ti(iso-PrO)4/L-diethyl tartrate/H2O cumene hydroperoxide, respectively. © 2001 Elsevier Science Ltd. All rights reserved.