Determination of molecular structure using vibrational circular dichroism spectroscopy: the keto-lactone product of Baeyer-Villiger oxidation of (+)-(1R,5S)-bicyclo[3.3.1]nonane-2,7-dione

reaction: see text] The Baeyer-Villiger oxidation of (+)-(1R,5S)-bicyclo3.3.1]nonane-2,7-dione, 1, can lead to four keto-lactone products, 2a-d. A single isomer is obtained experimentally. We have used IR and VCD spectroscopies to identify the structure of this product. DFT calculations of the IR and VCD spectra of 2a-d show unambiguously that the experimental product is (+)-(1R,6R)-2a, and not the expected product 2b. NMR studies, including comparison of DFT and experimental 1H and 13C spectra, support this conclusion. This work provides the first example of the use of VCD spectroscopy to discriminate between structural isomers of a chiral molecule. The specific rotation of (+)-(1R,6R)-2a, predicted using TDDFT methods, is negative demonstrating that absolute configurations determined from TDDFT calculations of specific rotations are not 100% reliable.