1,2-Dioxetanes intramolecular transformations

Nevertheless, there are two highly efficient CL systems which are believed to involve the CIEEL mechanism in the chemiexcitation step, i.e. the peroxyoxalate reaction and the electron transfer initiated decomposition of properly substituted 1,2-dioxetanes (Table 1)17,26 We have recently confirmed the high quantum yields of the peroxyoxalate system and obtained experimental evidence for the validity of the CIEEL hypothesis as the excitation mechanism in this reaction. The catalyzed decomposition of protected phenoxyl-substituted 1,2-dioxetanes is believed to be initiated by an intramolecular electron transfer, analogously to the intermolecular CIEEL mechanism. Therefore, these two highly efficient systems demonstrate the feasibility of efficient excited-state formation by subsequent electron transfer, chemical transformation (cleavage) and back-electron transfer steps, as proposed in the CIEEL hypothesis. 

The intramolecular chemical titration is conceptually and experimentally simple and convenient, but it requires that a particular dioxetane must be made that chemi-energizes the photochemically active carbonyl product K. This is usually a formidable and challenging synthetic problem. Representative intramolecularly chemienergized photochemical transformations include Norrish Type I cleavage (Eq. 44), Norrish Type II (Eq. 45a, b, c) cleavages, cyclohexadienone rearrangement (Eq. 46), and cyclopentenyl ketone rearrangement (Eq. 47). 

Compared to the intramolecular process, the intermolecular process is considerably more convenient and valuable because any dioxetane can serve as the chemienergization source and not that a specific dioxetane has to be tailor-made to release a particular photochemical transformation. Of course, an obvious requirement is that the chemienergized carbonyl product K possesses a high enough excitation energy so that energy transfer to the photochemically active acceptor... 

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