Z-E photoisomerization of benzylidenebenzocyclobutenones via ketene- allene intermediates. A laser flash photolysis study

Article abstract of DOI:10.1016/0040-4039(94)88151-0

Benzylidenebenzocyclobutenones I-E and I-Z undergo photoinduced isomerization via the intermediacy of ketene-allene II which in acetonitrile has a lifetime of ~26 μs and can be trapped with water and methanol. Trapping by the latter occurs with a rate constant of 1.2 x 10⁴ M^-1 s^-1 and leads to the expected ester. In addition to Z = E isomerization, product studies reveal the formation of dimeric products in very low quantum yields.