Triethylamine-Promoted Henry Reaction/Elimination of HNO2/Cyclization Sequence of Functionalized Nitroalkanes and 2‑Oxoaldehydes: Diversity-Oriented Synthesis of Oxacycles

The triethylamine-promoted cascade Henry reaction/elimination of HNO2/cyclization reaction of 2-oxoaldehydes with nitroalkanes bearing various remote functionalities is described. Both chiral and achiral nitroalkanes were applicable to this protocol, leading to a variety of oxacycles, such as chromenes, chromanes, cyclic hemiacetals, and polycyclic acetals. An unexpected regioselective photooxygenation occurred without sensitizer during derivatization to convert a derived diene product into a dioxetane by reaction with singlet oxygen, which provided chromen-2-one and benzaldehyde after fragmentation.