New deconjugation reaction of (E)-1-indanylidene methylarene brought by photolysis with protic acid

A new photodeconjugation reaction of (E) indanylidene methylarenes (1a–d) carried out by photolysis in the presence of protic acid are reported with 80% to >95% yields. The reaction mechanism is through the protonation of the less stable (Z) isomer to form stable indanyl cation followed by deprotonation.