Studies on 5-8 Fused Ring Compounds. V. The Conformations of Eight-Membered Rings in 5-8-5 Fused Ring Compounds and Their cis-trans Isomerization

Abstract

Abstract The 5-8-5 fused ring compounds, synthesized by photocycloaddition, cis-cisoid-cis- and cis-transoid-cis-tricyclo[9.3.0.04,8]tetradecane-2,9-dione (1-A and 2-A) and cis-cisoid-cis-tricyclo[9.3.0.03,7]tetradecane-2,9-dione (3-A) were isomerized to trans isomers (1-B, 1-C, 2-B, 2-C, and 3-B) at ring junction under basic conditions. Their molecular structures except for 1-B were determined by X-ray crystallography. The eight-membered rings of these 5-8-5 fused ring compounds were found in various conformations, boat-chair, twist-boat (S4), chair, twist-boat-chair, and chair-chair forms. With regard to the conformations of their eight-membered rings the strain energies were calculated by MM2 and the predicted conformations were compared with those obtained by X-ray crystallography.