Synthesis and structure of large difluoromethylene containing alicycles by ring closing metathesis (RCM)

Cyclotetra- and cyclohexa-decane ring systems were prepared with CF2 groups spaced 1,4- and 1,6- for tetradecanes together with 1,5- and 1,6- for hexadecanes. These alicyclic systems were assembled by ring closing metathesis reactions of long terminal diolefins. Ring cyclisation by RCM was promoted by the introduction of the dithiane motif, using a sulfur compatible metathesis catalyst. This gave rise to macrocyclic E-cycloalkanes, which were hydrogenated also using a sulfur compatible catalyst. Finally the dithianes emerged as appropriate precursor motifs for the introduction of difluoromethylene groups. X-Ray structures revealed that the resultant rings have the CF2 groups located only at corner positions and that these groups dictated the overall macrocyclic ring conformations.