When the alkene of compound 4 is isomerized, the two planes Csp 3 -Csp 2 -H on both sides of the alkene rotate both clock-and counterclockwise to form P-and M-cyclooctenes 5 and 6, respectively. In these cases, the resulting TCOs adopt a half-chair-chair conformation where the acetoxy group occupies an axial position in the P-isomer 5 and an equatorial position in the M-isomer 6 (Scheme 2). Next to the exo-derivatives, the endo-TCO analogues 13 and 14 were synthesized utilizing the same synthetic methodology (Scheme 1, endo-pathway). The iodohydrin step was performed on 2 and afforded 9 diastereoselectively in 82% yield. The endo-TCO-precursor 10 was obtained after dehydroiodination with DBU and subsequently isomerized into the corresponding endo-TCOs 11 and 12 in a 1:1 ratio. Similar to the exo-pathway, we obtained an inseparable mixture of the equatorial and axial diastereomers 11 and 12. Unfortunately, after ethanolysis with potassium carbonate an inseparable mixture of the two diastereoisomers 13 and 14 was obtained.