Circular dichroism spectra of trans-chalcone epoxides

The electronic absorption and CD spectra of (−)-trans-chalcone epoxide and its derivatives with methyl and alkoxy substituents at the ortho-positions of the aromatic rings have been measured. The spectra have been assigned with help of the energies, oscillatory strengths, and rotatory strengths of the singlet transitions obtained from DFT calculations. The features of the CD spectra, indicative of the absolute configuration, are the carbonyl n–π∗ band and two further strong bands assigned to the overlapping signals of π–π∗ and nepoxy–π∗ excitations.

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(2R,3S)-2,3-Epoxy-1-(2-tolyl)-3-phenylpropan-1-oneC16H14O2Ee = 71% (1H NMR with Eu(hfc)3)[α]D22=-166.9 (c 1, CH2Cl2)Source of chirality: asymmetric synthesis by chiral catalystAbsolute configuration: (2R,3S) (assigned by CD spectroscopy)

(2R,3S)-2,3-Epoxy-1-(2-methoxyphenyl)-3-phenylpropan-1-oneC16H14O3Ee = 83% (1H NMR with Eu(hfc)3)[α]D22=-98.5 (c 1, CH2Cl2)Source of chirality: asymmetric synthesis by chiral catalystAbsolute configuration: (2R,3S) (assigned by CD spectroscopy)

(2R,3S)-2,3-Epoxy-1-(2-ethoxymethyloxyphenyl)-3-phenylpropan-1-oneC18H18O4Ee = 70% (1H NMR with Eu(hfc)3)[α]D22=-102.3 (c 1, CH2Cl2)Source of chirality: asymmetric synthesis by chiral catalystAbsolute configuration: (2R,3S) (assigned by CD spectroscopy)

(2R,3S)-2,3-Epoxy-1-(2-isopropoxyphenyl)-3-phenylpropan-1-oneC18H18O3Ee = 79% (1H NMR with Eu(hfc)3)[α]D22=-131 (c 1, CH2Cl2)Source of chirality: asymmetric synthesis by chiral catalystAbsolute configuration: (2R,3S) (assigned by CD spectroscopy)

(2R,3S)-2,3-Epoxy-1-phenyl-3-(2-tolyl)-propan-1-oneC16H14O2Ee = 76% (1H NMR with Eu(hfc)3)[α]D22=-75.7 (c 1, CH2Cla2)Source of chirality: asymmetric synthesis by chiral catalystAbsolute configuration: (2R,3S) (assigned by CD spectroscopy)