Ethylene Dications Substituted with Electron-Donating Groups

Article abstract of DOI:10.1021/jo00283a012

Direct spectroscopic observations were made of substituted ethylene dications bearing ?-stabilizing groups such as an aryl, a hydroxy, or a methoxy group in a strong acid, trifluoromethanesulfonic acid (TFSA).Based on the spectroscopic evidence, we reached the following conclusions. (1) 1,1-Diaryl-2-hydroxy-2-methoxyethylene dications, 1,1-diaryl-2,2-dihydroxyethylene dications, and 1,1,2-triaryl-2-hydroxyethylene dications are discrete intermediates in the electrocyclization reaction to yield the fluorene and phenanthrol in TFSA. (2) Several dications bearing methoxy substituents on the aromatic rings are formed in trifluoroacetic acid (TFA). (3) NMR spectra suggested the nonplanar structures of O-protonated α-carbonyl diarylmethyl dications at the central C-C bond. (4) 1,2-Diaryl-1,2-dihydroxyethylene dications and 1-aryl-1,2,2-trihydroxyethylene dications are very stable.Ab initio MO calculations showed that 1,2-dihydroxyethylene dications are more stable than 1,1-dihydroxyethylene dications.