Journal of the American Chemical Society, Vol.118, No.29, 6890-6896, 1996
Stereochemistry and Conformational Anomalies of 1,2,3-Polycyclohexylcyclohexane and 1,2,3,4-Polycyclohexylcyclohexane
1,2,3-Tricyclohexylcyclohexane (3) and 1,2,3,4-tetracyclohexylcyclohexane (4) were synthesized by catalytic hydrogenation of 1,2,3-triphenylbenzene and 1,2,3,4-tetraphenylbenzene, respectively. The systems provide examples of three conformational anomalies : axial/equatorial, twist-boat/chair, and eclipsed/staggered stability reversals. Two axial substituents are present in the lowest energy conformational of cis,trans-3. The substituents in all-cis-3 are arrangement with the central ring. In all-trans-3 two substituents are gear meshed, which results in a nonstaggered arrangement. The central ring in cis,trans,cis-1,2,3,4-tetracyclohexylcyclohexane exists in a chair conformation while in the cis,trans,trans isomer this ring adopts a twist-boat conformation.