Photochemical aromatic substitution

Nitrophenyl ethers capable of undergoing photochemical nucleophilic aromatic substitution (Cornelisse et al., 1975, 1979 Comelisse and Havinga, 1975 Havinga and Comelisse, 1979) are recent additions to the list of photochemical reagents (Jelenc et al., 1978 Fig. 2.8). 

Reaction occurs via a shortlived triplet excited state, at rather low quantum efficiency, and appears to be quite selective for amino groups (Jelenc et al., 1978). This reaction has been used to label a galactose 

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The next three chapters are by Inoue and Mori, Albini, and Rossi, and deal with alkene photoisomerization reactions, the modification of benzylic positions and photochemical aromatic substitution reactions. (E)-2-cyclo-heptenone is produced upon irradiation of the Z-isomer at — 50 °C and can be trapped by cyclopentadiene to afford the adduct 13 [13]. Benzyl-substituted dihydroisoquinolinium derivatives can be used for the photochemical synthesis of tetrahydroisoquinolines. The corresponding... 

Photochemical aromatic substitution initiated by a reductive step as in SRN1 reactions can be used for the synthesis of cephalotaxinone (15). The corresponding iodoketone precursor cyclizes in liquid ammonia under photolysis [15]. 

Methoxy-l-nitronaphthalene (73a) and 1-nitronaphthalene (73b) undergo photochemical aromatic substitution reactions with cyanide (Scheme XXVIII). A two-fold increase in the quantum yield for the reaction is observed for (73a) when the reaction occurs in HDTC1 compared to aqueous solution 73). However, a 6800-fold catalytic increase in quantum yield is observed for (73b). SDS micelles decrease the quantum yield compared to aqueous solutions. The higher local concentration of cyanide near the HDTC1 micelles can explain a least partially the increase in quantum yield. However, the 6800-fold increase for (73b) is also due to a polarity effect on the reaction. This was demonstrated by an increase in the quantum yield of the reaction with decreasing polarity. 

Photochemical Aromatic Substitution Reactions 6.4.1 Nucleophilic Substitution... 

Fig. 6-7 Rationalization of Photochemical Aromatic Substitution (The brackets identify the less common or unobserved reaction.)...

Photochemical aromatic substitution, in Handbook of Organic Photochemistry and Photobiology, 2nd edn (eds W. Horspool and F. Lend), CRC Press, Boca Raton, pp. 37/1-37/14. 

Cornelisse, J., Photochemical Aromatic Substitution, in CRC Handbook of Photochemistry and Photobiology, CRC Press, Boca Raton, FL, 1994, 250. 

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