Abstract: The solid-state and solution photochemistry of seven compounds possessing the basic 1-oxy-cis-4a, 5, 8, 8a-tetra-hydronaphthoquin-4-01 structure has been investigated. In solution all seven substrates afford high yields of the corresponding [2+ 21 cage photoproducts when irradiated. On the other hand, for five of the substrates, photolysis in the solid state yields only traces of the cage compounds; instead, photoproducts are formed ...