Balz-Schiemann reaction photochemical

Photochemical modification of the Balz-Schiemann reaction has enabled fluorine-containing biologically important molecules e.g., imidaz-... 

Decomposition of Arenediazonium Tetrafluoroborates under Irradiation (Photochemical Balz-Schiemann Reaction)... 

Besides thermal decomposition of diazxvnium tetrafluoroborate salts (fluorodediazoniation), the Balz-Schiemann reaction can be carried out under either photochemical or ultrasonic irradiation. 

Methyl (5)-2-(Acetylamino)-3-(2-fluoroimidazol-5-yl)propanoate (a-A -Acetyl-2-fluoro-L-histidinc Methyl Ester, 21) Typical Procedure for the Photochemical, One-Pot Balz-Schiemann Reaction ... 

The photochemical Balz-Schiemann reaction has been used for the preparation of interesting fluoroarenc pharmaceutical agents, such as ring-fluorinated tyraminc and dopamine derivatives (Table 9. entries 1-3), and 2-, 5-, and 6-fluoronorepinephrine precursors (entries 4 and 5), from the corresponding nitroarenes. 

Several fivc-mcmbered-ring fluoroheteroaromatics, such as 4-fluoroimidazoles/ 4f° 2-fluoroimidazoles (e.g., 21),66 and 3-, 4- and 5-fluoropyrazoles,6 have been synthesized in 10-39 % yield via the Balz Schiemann reaction by photochemical irradiation of the corresponding diazonium salts in tetrafluoroboric acid solution (see Vol. ElOa, p 719ff). 

Photochemical Balz-Schiemann reaction of diazonium fluoroborates continues to be the method of choice to prepare fluoro substituted imidazoles. Thus, 4(5)-fluoroimidazole 1565 is prepared from 4(5)-nitroimidazole 1559 in moderate yield by conversion of the nitro group to the diazonium salt followed by irradiation in aqueous tetrafluoroboric acid. Sugar-fluoroimidazole derivatives 1566 and 1567 were prepared using an iV-silyl derivative of 1565 (Scheme 404). 

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