Photoactive cyclophanes, I. Synthesis, photophysical and photochemical properties of cinnamophanes

In order to transfer the so‐called topochemical control established by Schmidt and coworkers to fluid solutions, the [2.2]paracyclophane framework was substituted with two acryloyl substituents, one on each of the two decks. The 4 products thus formed are termed cinnamophanes. The pseudo‐gem derivative, 1, was shown to undergo a very efficient stereospecific [2 + 2] photocycloaddition to form 5 with the highest quantum yield (0.8) ever observed for such a reaction. Whereas 2, 3 and 4, the regioisomers of 1, undergo a trans‐cis photoisomerisation, compound 1 leads to the photocycloadduct as the sole photoproduct. This unusually fast cycloaddition reaction is not sensitive to oxygen and is largely unaffected by temperature variations. It is believed to be a singlet state reaction. The synthesis and a spectroscopic (absorption and fluorescence emission) study of 1–4 and 5 are described.