The Radical Ions of Indolizino [6,5,4,3‐aij]quinoline and Some of its Derivatives

Indolizino [6,5,4,3‐aij]quinoline (1) and its 3,9‐dimethyl‐ (2), di‐tert‐butyl‐ (3) and diphenyl‐(4) derivatives yield persistent radical cations which have been studied by ESR and ENDOR spectroscopy. The corresponding radical anions have also been prepared, but only that of 3 was amenable to a complete characterization by hyperfine data. The π‐spin populations in the radical anions are essentially localized on the 13‐membered C‐perimeter, and thus both the HOMO and LUMO of 1 exhibit an ‘annulenyl character’. The radical anions of 1 and 2 have gradually been converted into those of the corresponding 3,4‐dihydro derivatives (1‐H2 and 2‐H2) which have been unambiguously identified by a combination of preparative and spectroscopic methods.