Generation and spectroscopic properties of syn-1,6:9,14-bismethanodicyclodeca[cd,gh]pentalene dianion

The hydrocarbon precursor, 8,16-dihydro-syn-1,6;9,14-bismethano[cd,gh]pentalene (5), to the title structure, dianion 4, was synthesized from ethyl 4-bromo-1,6-methano[10]annulene-3-carboxylate (6) in three steps, which included a nickel-catalyzed stereoselective homo-coupling, LiAlH4 reduction of the ester groups, and scandium triflate-catalyzed double intramolecular cyclization of the biarylmethyldiol. Deprotonation of 5 with n-butyllithium in THF-d8 provided 4, whose structure was confirmed by NMR analysis. Aspects of chemical shifts in the 1H NMR spectrum and the calculated structure of 4 establish its diatropic nature.