engleski

Chromatographic resolution, Circular Dichroism Spectra, Absolute Configurations, and Crystal Structures of Bridged Biphenyls, Containing Sulfide, Sulfoxide, and Sulfone Groups in the Bridge

Four chiral 1, 1'-biphenyls with one or two sulfur-containing bridges in 2, 2'-or 2, 2'- and 6, 6' position, viz. 1, 11-dimethyl-5, 7-dihydrodibenzo/c, e/thiepin (1), its S-oxide (2) and S, S-dioxide (3), and the doubly bridged 10, 12-dihydro-4H, 6H-/2/benzothiepino/6, 5, 4-def//2/benzothiepin (4) have been studied by chromatography, CD spectroscopy, X-ray crystallography, and empirical force-field and CNDO/S calculations. The structures obtained by force-field calculations showed good agreement with the crystal structures determined for 2 and 3. Compounds 2, 3 and 4, but not 1, could be resolved into enantiomers by chromatography on swollen microcrystalline triacetylcellulose. The barrier for biphenyl inversion in 2 was found to be higher than 167 kJmol^-1 by an attempted thermal racemization. The CD spectra of the enantiomers of 2-4 were recorded and resolved into individual bands, and the corresponding rotational strengths were calculated. The transitions showed considerable similarity to those of a 1, 1' biphenyl with hydrocarbon bridge (cf. 5), albeit with bathochromic shifts, which permitted the assignment of the absolute configurations of the enantiomers of 2-4. The assignments were supported by comparison of the experimental CD spectra with spectra calculated by the CNDO/S method. All first-eluted enantimers were found to have the (S)-configuration.

Circular Dichroism Spectra ; Absolute Configurations ; Bridged Biphenyls ; X-ray cryctallography ; empirical force-field calculation ; CNDO/S calculation ; Enantioselective chromatography on triacetylcellulose

nije evidentirano