Photoredox reaction intramolecular

Photoredox reactions occur either via imermolecular or via intramolecular processes. The most general scheme of an intermolecular photoredox reaction (Rehm and Weller, 1970) is shown in reaction 1 A compound C undergoes a transition from the ground state to an electronically excited state by absorption of light, C - C. If such an excited compound encounters a reaction partner Q (either an electron donor or an electron acceptor), electron transfer may take place, leading to C+ and Q ... 

While intramolecular photoredox reactions of CTTL excited states appear to be relatively unimportant, there is considerable evidence that these states can undergo bimolecular electron transfer with high quantum efficiency. Examples of this type of process are given in equations... 

Ruthenium (II) polypyridyl complexes promote the photoredox reactions such as Diels-Alder reaction (see formulae 29 31) and azomethine ylide formation followed by [3 + 2] cycloaddition (32-34) by use of visible light. Yoon found 2,2 -bipyrazine ligand is better than 2,2 -bipyridine. Bach reported enantioselective intramolecular [2 + 2] and intermolecular [3 + 2] photocycloaddition by use of chiral hydrogen bond templates (37) and (41). ... 

The vanadium(V) oxo complex, [VO(S2CNMe2)3] (714), has been shown to sensitize the polymerization of styrene when irradiated at X 365 nm (715). A spectroscopic analysis shows that initiation occurs primarily through loss of a dithiocarbamate radical via an intramolecular photoredox reaction, with [VO(S2CNMe2)2] being the final photoproduct. The rate of polymerization is proportional to the square root of [VO(S2CNMe2)3] concentration. 

In summary, the photolysis of aqueous [(NH3)50s (N2) Os (NH3)5] induced by MLCT excitation leads to the reductive splitting of the bridging N2 ligand yielding [0s (NH3)4N] as main photoredox product. It should be emphasized that the electronic CT excitation does not only provide a suitable intramolecular redox reaction but may supply also the necessary energy for activation and cleavage of the very stable N2 molecule. 

Photoredox catalysis was utilized by Rueping et al. to effect the intramolecular C—H functionalization of tertiary amine 114. When conducted in the presence of oxygen, indole 115 was isolated as the major product in good yields. Depending on the substrate and reaction conditions, tetrahy-droquinohne derivatives or substituted anilines could also be obtained (13JA1823). 

The asymmetric reduction of y-phenylseleno ketones and the intramolecular substitution of the phenylselenone residue by the oxygen atom of a hydroxy group led to 2-substituted tetrahydrofurans (13OL3906). Polysubstituted furans were formed in the photoredox neutral coupling of alkynes with 2-bromo-1,3-dicarbonyl compounds. The reaction was carried out without any external stoichiometric oxidants (130L4884). 

Ru Many examples of radical arylations by photoredox catalysis have been recently reported [62-64]. For instance, when ArN +X salts are reduced, a C—N bond cleavage occurs to give Nj, an Ar radical, and the anion X . An intramolecular photo-Pschorr reaction is exemplified by the conversion of ArN +X (89) into phenanthrene derivatives 92, in quantitative yields, photocatalyzed by [Ru(bpy)3](BF )j (Scheme 9.12). In this way, the excited state of this ruthenium complex was able to reduce the salt 89 to the corresponding aryl radical 90. This in turn cyclized, thereby... 

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