Synthesis of a novel non-benzenoid quinone, 3,10-dihydro-2,4-dimethyl-7,13- methanocyclohepta[11]-an nulene-3,10-dione, from 8H-7,9-bis(methoxycarbonyl)-5, 11-methano[11]annuleno[c]furan-8-one

8H-7,9-Bis(methoxycarbonyl)-5,11-methano[11]anuleno[c]furan- 8-one (3) undergoes [4+3] cycloaddition with an oxyallyl species generated from 2,4-dibromo-3-pentanone in the presence of KI and copper, followed by dehydration in fluorosulfuric acid to give cyclohepta[11]annulenedione diester 9. After hydrolysis of the ester groups, decarboxylation yielded the title quinone 6. The 1H NMR spectrum of 6 in D2SO4 indicates generation of its protonated dicationic species.