One-pot access to push-pull oligoenes by sequential [2 + 2] cycloaddition-retroelectrocyclization reactions.

The formal [2 + 2] cycloaddition-retroelectrocyclization reaction was employed as the key transformation to obtain donor-substituted, π-conjugated polycyanohexa-1,3,5-trienes (TCHTs and PCHTs) and polycyanoocta-1,3,5,7-tetraenes from donor-substituted tetracyanobuta-1,3-dienes (TCBDs) and electron-rich alkynes. These push-pull-substituted oligoene chromophores were also accessed in good yield from tetracyanoethylene and donor-substituted alkynes by using a one-pot protocol. All bis-(N,N-dialkylanilino) donor-substituted push-pull trienes and tetraenes showed better electron-accepting potency and lower HOMO-LUMO gaps than the corresponding TCBDs, as evidenced by optical and electrochemical studies.