Hydrocarbon Analogue of the Squarate Dianion. Evidence for Its Possible Aromaticity and the Examination of Its Behavior with Two Quenching Agents.

Article abstract of DOI:10.1021/jo00265a012

The hydrocarbon analogue of the squarate dianion 2 was prepared by metalating 1,2-dimethyl-3,4-bismethylenecyclobutene with n-butyllithium/potassium tert-butoxide or n-butyllithium/TMEDA.The "dianion" was characterized by quench with n-butyl chloride or methyl iodide, which revealed a maximum concentration of dianion after 144 h when the starting alkene was metalated with n-butyllithium/TMEDA.The dianion was also characterized by 1H NMR spectroscopy, which showed a singlet at 1.71 ppm in THF.The linear relationship between charge density and chemical shift for the cyclic aromatic ions is also demonstrated by 2, suggesting its possible aromaticity.The quench with methyl iodide showed significantly more coupled products than did the quench with n-butyl chloride even when the counterions were lithium TMEDA.