AbstractPhotosensitized cycloaddition of 4,6‐dimethyl‐2‐pyrone (1) with methacrylonitrile (3b) afforded two types of [2 + 2]cycloadducts, 4b and 6b, across the C5‐C6 and C3‐C4 double bonds in 1, respectively. Photosensitized reactions of 1 with dimethyl maleate and dimethyl cyclobutene‐1,2‐dicarboxylate gave [2 + 2]cycload‐ducts 4d, 4e across the C5‐C6 double bond, in addition to [4 + 2]cycloadduct 9d or bicyclo[4.2.0]octadiene 10e. The photoreactions of methyl 2‐pyrone‐5‐carboxylate (2) with 3b and 2‐chloroacrylonitrile (3c) gave [4 + 2]cycloadducts 5b, 5c in addition to [2 + 2]cycloadducts 11b and 11c across the C5‐C6 double bond in 2. The photocycloaddition mechanism was explained from results calculated by means of PM3‐CI method. Namely, the site‐ and/or regio‐selective products, 4, 5, 8, 9 and 10 were thought to come from the same site‐selective radical intermediates in the case of electron‐poor olefins. Pyrolysis and/or hydrolysis of the cycload‐ducts 4e, 5b, 5c gave 5,6‐dihydro‐2‐pyrone 12 or benzene derivatives.