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-thi ochroman S-oxide 1 using vibrational circular dichroism (VCD) spectroscopy. The VCD spectrum of a CCl4 Solution of 1 was analyzed using density functi onal theory (DFT). which predicts three stable conformations of 1. separate d 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 exce llent agreement with the experimental Spectrum of (+)-1. The absolute confi guration of 1 is therefore (R)-(-).(S)-(divided by). (+)-1 and (-)-1 of hig h 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 tartrat e H2O cumene hydroperoxide, respectively. (C) 2001 Elsevier Science Ltd. Al l rights reserved.