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'-positions, viz. 1,11-dimethyl-5,7-dihydrodibenzo[c,e]t hiepin (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 empi rical force-field and CNDO/S calculations. The structures obtained by force -field calculations showed good agreement with the crystal structures deter mined for 2 and 3. Compounds 2, 3, and 4, but not 1, could be resolved into enantiomers by chromatography on swollen microcrystalline triacetylcellulo se. The barrier for biphenyl inversion in 2 was found to be higher than 167 kJ . mol(-1) by an attempted thermal racemization. The CD spectra of the e nantiomers 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 bridg e (cf: 5), albeit with bathochromic shifts, which permitted the assignment of the absolute configurations of the enantiomers of 2-4. The assignments w ere supported by comparison of the experimental CD spectra with spectra cal culated by the CNDO/S method. All first-eluted enantiomers were found to ha ve the (S)-configuration.