Sesquifulvalene Trapping as a [12+2] Adduct with Tetracyanoethylene

Sesquifulvalene (1) is a substance of considerable theoretical interest¹ which is expected to have a significant contribution to its structure from the dipolar resonance form 1b,² and hence an exceptionally low bond order for the central double bond. Although a wide variety of annelated and otherwise substituted sesquifulvalenes have been prepared and characterized,³ the parent substance has proved remarkably elusive. Very recently, a preparation of 1 in crystalline form has been reported, based upon elimination of an acetoxy-11,12-dihydrosesquifulvalene derivative.⁴