Photoinduced electron transfer process, phthalimides

To justify the experimental result we could follow the stepwise mechanism discussed in the previous section. The phthalimide system is a good electron acceptor in the excited state and the alkylsilane can be an electron donor, so a photoinduced electron transfer process could lead to the charged separated diradical 13. Transfer of the electrofugal TMS group to the oxyanion carbonyl oxygen would form azo-methyne ylide 14 that can be trapped by the mefliyl acrylate to yield the endo-reaction product 12 (Scheme 16.9). 

Electronically excited phthalimides can act as good electron acceptors and carboxylic acids are documented to serve as electron donors in photoinduced SET reactions. It is likely then, that in the excited state, an electron transfer process between the phthalimide system and the carboxylic acid would occur, leading to charge-separated diradical 6. Proton transfer from the carboxylic acid function (iT" is an electrofugal group) would form a carboxy radical 7, which could undergo rapid decarboxylation to azomethyne ylide 8. This reactive species is transformed into the final decarboxylated product 3 by intramolecular proton transfer (Scheme 16.4). 

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