Biradicals/zwitterions from enallene-isonitriles.: Formal [4+1] cycloadditions leading to 11H-indeno[1,2-b]quinoline and related compounds

[GRAPHICS] 1,3-Prototropic rearrangement of the benzannulated enyne-isonitriles to the corresponding enallene-isonitriles followed by cycloaromatization generated the putative quinoline biradicalslzwitterions. A subsequent intramolecular radical-radical coupling or electrophilic aromatic substitution then gave the formal [4 + 1] cycloaddition adducts leading to 11H-indeno[1,2-b]quinoline and related compounds.