Photolysis of 4-methyl-1-oxoanhydroberberine (9) in the presence of nitrosobenzene gives two isomeric photoadducts (11) and (12). In the presence of diethyl azodicarboxylate, 9 affords two different types of photoadduct (13) and (14). These photoadducts are considered to be formed by the photochemically allowed [2s+2s+2+s] cycloaddition reactions.
