A mild and efficient method of aromatic fluorination

Synthesis of radioiodinated analogs of 2‐phenylpyrazolo[4,3‐c]‐quinolin‐3 (5H)‐one by a modified triazene method

“…The n i t r o compounds (5) and (6) were synthesized, according t o a method described by Yokoyama e t a1 ( 2 ) , by t h e r e a c t i o n s of e t h y l 4-chloroquinolin-3-carboxylate (3) and e t h y l 4-chloro-6-nitroquinolin-3-carboxylate (4) with p-nitrophenylhydrazine and phenylhydrazine, r e s p e c t i v e l y . The amino intermediates (7) and (8) obtained by reduction with sodium s u l f i d e were then d i a z o t i z e d using sodium n i t r i t e and methanesulfonic a c i d and t h e diazonium s a l t s on coupling with excess of p i p e r i d i n e and p y r r o l i d i n e gave t h e expected t r i a z e n e (9) and (10) i n 47 and 89% y i e l d s , r e s p e c t i v e l y , a f t e r column chromatography. s t o r e d a t room temperature.…”

Aromatic Fluorination by Decomposition of Triazenes in Ionic Liquids

“…14,15,18 The four aryl amines we selected have acetyl, methyloxycarbonyl, phenyl, and isopropyl groups in para position. From prior studies, it is known that the diazonium ion derived from triazene with electron deficient substituents on the aromatic ring would undergo decomposition via a radical path, whereas the diazonium ion derived from triazenes with electron rich substitutents would decompose predominantly via a heterolytic decomposition.…”

“…Other chemicals were purchased from Aldrich Chemical Co. Triazenes were prepared by known methods. 14,15,18 The products 2 and side products 3 16,17 were identified by comparison of their physical properties with those for these materials reported in the literature.…”

“…However, because all of these aryl diazonium salts are relatively unstable, aryl triazenes, which are easily prepared from aryl diazonium chlorides and alkylamines, have been used as precursors for aromatic fluorination. [14][15][16][17][18] In fact, this method, which has been called the "Wallach reaction", based on the name of the lead author of the original report of this method, and it predates the Balz-Schiemann reaction. 19,20 The fluorination of aryl triazenes can be affected by their thermal decomposition in acidic medium in the presence of fluoride ion.…”

Carbon-Fluorine Bond Formation for the Synthesis of Aryl Fluorides

“…Other variations involve fluorodediazoniation in HF/pyridine and in BF 3 ·Et 2 O,38 the use of triazenes in HF/pyridine as precursors to aryldiazonium salts,39 and fluorodediazoniation in ionic liquids 40…”