Single electron transfer phthalimides

N-Phthalimide-linked peptides that contain C-terminal a-amidotrimethylsilyl groups undergo macrocyclization reactions via sequential single-electron transfer processes [11, 12]. Thus, electron transfer from the neighboring amide to the excited phthalimide chromophore leads to an amide radical cation. Hole migration to the ot-amidotrimethylsilane center is followed by desilylation to form an 1, co-biradical intermediate, which finally cydizes to the macrocydic peptide (Scheme 9.9). 

Phthalimides. Like their aromatic ketone counterparts, TV-alkyl phthalimides participate in hydrogen atom abstraction reactions to form a large variety of heterocyclic compounds. However, despite many similarities between phthalimides and aromatic ketones, there are some important differences. In contrast to aromatic ketones, electronically excited phthalimides are not transformed quantitatively into the triplet state, and thus they may react from both the singlet and the triplet state. In addition, phtalimides are much more inclined to photoinduced single-electron-transfer (PET) reactions [24,25]. (For details see Sec. 3.3.2.1.)... 

Intramolecular single electron transfer occurs within the supramolecular systems (224). " The electron transfer only occurs from the nitrogen function attached to the 4-amino substituent. A comparison between redox potentials and the photophysical behaviour of the phthalimides (225) has been made. Other work dealing with electron transfer in phthalimide systems has examined the behaviour of (226). The singlet excited state of (227) is fluorescent and this can be effectively quenched by ferrocene. ... 

Lactams such as (258) can be synthesized from the phthalimides (259) by irradiation. Again the reactions are controlled by single electron transfer processes that are usually encountered in the photochemical reactions of phthalimides. The outcome of the reaction is a conventional proton transfer from the benzylic site within the zwitterionic biradical formed on irradiation. Cyclization within the resultant 1,5-biradical affords the final product. Griesbeck and his coworkers have studied the photochemical reactivity of the phthalimide derivatives (260). These compounds on irradiation under triplet sensitized conditions undergo decarboxylation and cyclization. The reaction involves SET and the key intermediates are shown as (261) and (262). The biradical anion (262) is the species that either cyclizes to afford (263) or abstracts hydrogen to yield (264). The reaction is controlled by a variety of factors that have been reported in some detail. Some photochemical reactions of phthaloylcysteine derivatives have been described. Typical of the processes are the decarboxylations of the derivative... 

Maruyama and Kubo have reported that the intramolecular photocyclization of the succinimide (180) gave the solvent-incorporated nine-membered ring (181) (Equation (16)). The mechanism has been described in terms of a photoinduced addition of methanol between electron acceptor (phthalimide moiety) and donor (alkene), involving initial single electron transfer from the alkenyl double bond to the phthalimide group <78JA7772>. 

In keeping with the seminal work of Kita, we proposed that the I(III)-mediated amination involved a radical cation intermediate that was generated by single electron transfer from the arene to the I(III) oxidant. The consequent radical cation should be highly reactive, and the attack of a phthalimide nucleophile would lead to a mixture of regiomeric products, like the 5 6 3 mixture that was observed for our toluene reaction (Scheme 10). This hypothesis contrasts with the mechanisms proposed by Chang and Antonchick, as electrophilic aromatic substitution, even with a reactive R2N species, should favor the para product. 

Phthalimides react with KOAc under photochemical conditions to undergo decarhoxylative addition of a methyl group (eq 43). These reactions proceed through single electron transfer from the carboxylate ion to the photoexcited phthalimide to generate the corresponding radical anion and the acetate radical that loses CO2 and releases the methyl radical that eventually combines with the phthalimide radical anion. 

ALPhthaloyl a-amino acids 1 undergo photodecarboxylation to generate the eorre-sponding ALalkylphthalimides 3. It is believed that the photodecarboxylation occurs by photoinduced single eleetron transfer (SET) involving the electronieally excited phthalimide as eleetron aeeeptor and the carboxylic acid as electron donor (Scheme 16.2). 

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