Add time:08/18/2019         Source:sciencedirect.com

3H-Cyclonona[def] biphenylene, 6, was deprotonated with n-butyllithium to form the mono-trans anion 7. This anion was fully delocalized and aromatic, with the interior proton having a 1H NMR absorption at -2.79 ppm. This downfield shift was attributed to the proton being in the middle of a ring with a large diamagnetic ring current, calculated to be +0.96 (relative to +1.00 for benzene). Molecular mechanics calculations predicted that 7 was not planar, the interior carbon and the attached proton come out of the plane to relieve severe Van der Waals interactions. Anion 7 was quenched with a variety of electrophiles to give products with the electrophile in the exo position. Attempted generation of the anion of 3-roethyl-3H-cyclonona[def]-biphenylene, 10, predicted to be less stable than anion 7 for both steric and electronic reasons, was unsuccessful. Instead, the n-butyllithium added to the π-system to give the stabilized benzylic anion, 13, which was quenched with methanol-d to give compound 14.

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