Enantioselectivity in visible light-induced, singlet oxygen [2+4] cycloaddition reactions (type II photooxygenations) of 2-pyridones.

3-Substituted 2-pyridones were enantioselectively (68-90% ee) converted into the respective 3-hydroxypyridine-2,6-diones by a sequence consisting of a template-mediated type II photooxygenation and an acid-catalysed rearrangement.