CD study of the chiral enamines 4-9 revealed the presence of the azastilbenelike chromophore, and exciton coupling between this chromophore (A) and aromatic chromophore B. Coupled excitons in 5 and 8 suggest M (--) absolute conformation between chromophores A and B. o 1996 Wiley-Liss, Inc.
KEY WORDS: circular dishroism (CD) study, exciton coupling, azastilbene chromophore, absolute conformation of coupled chromophores Continuing our study of catalytic properties of metal complexes of chiral 1,Sbisnitrogen ligands obtained from 242'pyrido)acetophenone and S( -)-1-phenylethylamine,' we prepared a series of chiral ligands 4-9. Some of their Cu complexes proved more effective in enantioselective cyclopro-panation2s3 than those from previously prepared 1,5bisnitrogen ligands.' The enhanced enantioselectivity was ascribed3 to increased crowding around the c h i d centre in the cyclohexylethylamine derivatives 6 and 9 and also to enhanced steric perturbations by the large planar subunit in the quinoline derivatives 7-9. In order to analyse completely the chromophore system in these chiral ligands, and to define their absolute conformation in solution, we prepared model compounds 6 and 9, without aromatic rings bound to chiral center. Herewith we describe the preparation and complete analysis of the chiroptical properties of the title compounds, which allowed the assignment of absolute conformations of these chiral ligands.
MATERIALSAND METHODS
Calculations
cedures in SYBYL software package of TRIPOS Associates.
Force field calculations were performed using standard pro-
General
Melting points were determined on an Electrothermal Melting Point Apparatus, in capillary tubes, and are uncorrected. 'H-and 13C-NMR spectra were registered in CDC13 on a Varian a 3 0 0 GEM spectrometer using TMS as internal standard. IR spectra were run on a Perkin-Elemer 297 spectrophotometer. Optical rotations were measured on an Optical Activity AA-10 Automatic Polarimeter in a 1 dm cell; concentrations are given in g/100 ml. UV/VIS and CD spectra were recorded in acetonitrile on a Jobin-Yvon VI dichrograph calibrated with epiandrosterone. Measurements were performed at room temperature in 0.02 and 1.0 cm cells.
Ketone 1 was prepared as described!