(Z)-2,2'-Disubstituted Bifluorenylidenes by Intramolecular Desulfurdimerization Reactions

Article abstract of DOI:10.1021/jo00293a038

W(CO)6-mediated intramolecular desulfurdimerization reactions have been used in the syntheses of bridged 2,2'-disubstituted bifluorenylidenes in satisfactory yields.Ring sizes from 12 to 24 can be synthesized by this reaction.The extension of this reaction for the synthesis of bifluorenylidene-hinged crown ethers is described.The X-ray structure of 6i has been determined.The two fluorenylidene moieties are each planar, making a dihedral angle of 44.9 deg.The first optically active bifluorenylidenes were unequivocally synthesized, and the barriers for the racemization of two such molecules have been determined (12 kcal/mol).The racemization process may arise from the pyramidalization at C₉ and/or C_9' followed by rapid twisting along the C₉-C_9' bond.