Dimethylsulfonium fluoren-9-ide: solution structure and dynamic behaviour of a semi-stabilised sulfonium ylide

The semi-stabilised ylide, dimethylsulfonium fluoren-9-ide, has been studied by variable temperature NMR and found to adopt a conformation in which the filled orbital on carbon is perpendicular to the lone pair on sulfur. The rotational barrier (ΔG‡) around the ylide C–S bond is found to be 42.0 ± 1.0 kJ mol–1.