Sensitized photocycloadditionreactions of polymethylenedioxy-di-2-pyrones (1 - 3) with ethylene diacrylate (4a) afforded macrocyclic dioxatetralactones (6a - 8a) having sixteen- to eighteen-membered rings. Similar reaction of 1 with ethylene dimethacrylate (4b) afforded similar lactones (6b) and (9). The stereochemical features of 6a and 7a depending on the chain length elucidated by the X-Ray crystal