Photochemical Di-π-Methane Rearrangement Reactions.

Photochemical di-π-methane (DPM) rearrangement, a classic transformation pioneered by Zimmerman, elegantly converts 1,4-dienes and related systems into complex, strain-rich vinylcyclopropane architectures. For decades, its utility in organic synthesis was constrained by its reliance on direct UV irradiation, which limited functional group tolerance and practical application. However, the recent integration of this elegant photochemical rearrangement with the principles of visible-light-mediated triplet energy transfer catalysis has sparked a dramatic renaissance. This review chronicles the journey of the DPM rearrangement from its foundational mechanistic principles to its modern catalytic incarnation. We detail the expansion of the reaction family-encompassing oxa- (ODPM) and aza-di-π-methane (ADPM) variants-and highlight its evolving applications in the total synthesis of natural products and beyond. Finally, we offer a perspective on future opportunities, underscoring how this venerable reaction continues to enable synthetic innovation and discovery in the 21^st century.