The photoreactions of 2-chloro-, 2-bromo-, 2, 3-dichloro-and 2, 3-bromo-1, 4- naphthoquinones with arylethenes are dependent on the addend structure. Cyclobutane adducts are formed from styrene, 1, 1-diphenylethene undergoes photosubstitution to give photolabile 1, 1-diphenyl-1, 3-diene derivatives, and spiro-oxetanes are the main products with trans-stilbene. 2-Acetoxy-1, 4-naphthoquinone undergoes efficient (2π+ 2π) ...