Intramolecular cycloadditions of aza-o-xylylenes generated via excited state intramolecular proton transfer (ESIPT) to furanacetic acid-based unsaturated pendants was shown to overcome the unfavorable energetics of the azetidinone ring formation, offering rapid access to β-lactams as primary photoproducts. These 2,3- and 3,4-dihydrofuran-containing reactive intermediates are suitable for a broad spectrum of postphotochemical transformations yielding complex polyheterocyclic molecular architectures possessing the β-lactam moiety.