The Use of Precise Structural Information for the Understanding of the Conformational Behavior of cis-5-(tert-Butylsulfonyl)- and cis-5(tert-Butylsulfinyl)-2-tert-butyl-1,3-dioxane

Article abstract of DOI:10.1021/jo00286a032

A single-crystal X-ray structure determination of the title sulfoxide (cis-2) was carried out and compared with data previously reported for the corresponding sulfone (cis-1).Whereas the latter adopts an eclipsed conformation (one S-C/C-H and two S=O/C-C eclipsed bond pairs), both the tert-butyl and the S=O group in the sulfinyl function point outside the ring in a staggered rotamer.A substantial difference in length for the endocyclic C-C bonds in cis-2 suggests the effect of through-space ?_C-C/?^*_S-O (attractive) and ?_C-C/n_S (repulsive) interactions and/or ?_C-H -> ?^*_C-S stereoelectronic mechanisms.The X-ray diffraction study of the cyclohexane analogue (cis-4) shows again a staggered conformation for the tert-butylsulfinyl group, but confirms the repulsive steric hindrance between the gauche t-BuS and endocyclic methylene groups.The contrasting behavior between the sulfone and sulfoxide groups points to the existence of an attractive interaction S=O/C-C, which stabilizes the eclipsed conformer in cis-1 and overcomes the torsional strain in the eclipsed bond pair S-C/C-H.The nature of the stabilizing S=O/C-C interaction is proposed in the light of recent theoretical calculations.