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‐dihydrodibenzoc,e]thiepin ( 1 ), its S‐oxide ( 2 ) and S,S‐dioxide ( 3 ), and the doubly bridged 10,12‐dihydro‐4H,6H‐2]benzothiepino6,5,4‐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 kJ⋅mol⁻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 enantiomers were found to have the (S)‐configuration.