Photochemistry of (‐)‐Levoglucosenone: Norrish Type I Reaction and Photoinduced Electron Transfer Processes

Photochemical reactions of levoglucosenone (LGO) considerably extend its potential as a synthon in organic synthesis. At the photochemical excited state, LGO undergoes a reaction that resembles Norrish type I reactions. Ketene intermediates are formed and trapped with alcohols or amines. A variety of alkenes with interesting substitution patterns are thus obtained. The reaction mechanism has been determined and compared to the classical mechanism of the Norrish type I reaction of Cyrene. The triplet energies of both compounds have also been determined by phosphorescence at low temperature. In the case of photochemically excited LGO, electron transfer from tertiary aromatic amines is possible. Such a photochemical electron transfer can also be induced by sensitization involving triplet energy transfer from a sensitizer to LGO. These processes are competitive with the efficient Norrish type I reactions. In such reactions, the bicyclic structure of LGO is conserved, and aniline derivatives are stereospecifically added.