A metal- and photocatalyst-free photoinduced radical cascade hydroalkylation of 1,7-enynes has been disclosed. The process is triggered by a single electron transfer (SET) event involving a photoexcited electron-donor-acceptor complex between an NHPI ester and a Hantzsch ester, which decomposes to afford a tertiary radical that is readily trapped by the enyne. The method provides an operationally simple, robust, and step-economical approach toward the construction of diversely functionalized dihydroquinolinones bearing quaternary centers. A sequential one-pot hydroalkylation-isomerization approach is also offered, giving access to a family of quinolinones. A wide substrate scope and high functional group tolerance were observed in both approaches.