Expanding the chemical space for push-pull chromophores by non-concerted [2+2] and [4+2] cycloadditions

Non-concerted [2 + 2] and [4 + 2] cycloadditions between N, N-dimethylanilino- substituted 1,1,2,4,4-pentacyanobuta-1,3-diene and 4-ethynyl-N,N-dimethylaniline are controlled by solvent polarity and provide access to a highly functionalised 6,6-dicyanopentafulvene featuring an intense, low-energy charge-transfer band and to an unusual spirocyclic zwitterion, characterised by X-ray analysis.