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)-(divided by). (+)-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. (C) 2001 Elsevier Science Ltd. All rights reserved.