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.