Hydrogen fluoride with triazenes

More convenient for the formation of aryl fluorides 4 is the decomposition of triazenes with hydrogen fluoride/pyridine (70 30 w/w) mixture, easier to handle than pure hydrogen fluoride. In this case, decomposition is performed at a lower temperature (18-50°C) and acetic acid, for example, is a suitable solvent.299 However, radical side reactions can be more pronounced, especially with bromo-, iodo-, nitro- or 2-methoxy-subslituted substrates. 

Halocinnolines can be prepared by treatment of polystyrene-bound (2-alkynyl-phenyl)triazenes with hydrogen chloride or hydrogen bromide (Entry 6, Table 15.27). This reaction involves the initial release of 2-alkynylphenyldiazonium salts into solution, which then cyclize to the halocinnolines. The corresponding 4-hydroxycinnolines are obtained as by-products in variable amounts. Hydrogen fluoride or hydrogen iodide do not lead to the formation of cinnolines [324]. 

A study concerning the yields of fluorination by acid decomposition of piperidinotriazenes from several anilines with hydrogen fluoride (anhyd HF, coned aq HF, or HF, pyridine) in various solvents, such as tetrahydrofuran, benzene, dichloromethane, and acetic acid, was carried out in order to establish the best reaction conditions for the [ F]fluorine labeling of estrogens. Hence, 2 -fluorohexcstrol dimethyl ether (4) can be obtained from triazene 3 using 49% aqueous hydrogen fluoride. ... 

Fluorotamoxifen (2) Typical Procedure for the Acid Decomposition of Aromatic Triazenes with 40 % Aqueous Hydrogen Fluoride 22... 

Fluoroaromatic Compounds by Acid Decomposition of Aromatic Triazenes with Hydrogen Fluoride/Pyridiiie General Procedure 21... 

---