Arylboronic acids fluorination

The same research group additionally presented further investigations on fluor-ous-phase palladium-catalyzed carbon-carbon couplings [93]. Fluorinated aryl octyl-sulfonates were reacted in slight excess with arylboronic acids under microwave con-... 

Trialkylaryltin derivatives 30 are converted into fluoro-substituted derivatives 31. 37-38 (4-Mcth-oxyphenyl)trimethylsilane (32) in acetonitrile gives 4-fluoroanisole and (3-fluoro-4-meth-oxyphenyl)trimethylsilane in the ratio 1 2. A -Methyldiethanol esters of arylboronic acids 33 (l-aryl-5-methyl-2,8-dioxa-5-azonia-l-boranuidabicyclo[3.3.0]octanes) are converted into tluoroaromatic compounds with cesium fluoroxysulfate in acetonitrile in the presence of 1,3-dinitrobenzene at room temperature.39-40 Regiospecific synthesis of 2-fluoro-3-0-methyles-trone in 27 % yield occurs upon fluorination of the corresponding arylboronic acid with cesium fluoroxysulfate.41... 

Fluorination of Alkenyiboron Compounds and Arylboronic Acids and Derivatives... 

Fluorination of Arylboronic Acids 15 in Methanol General Procedurc ... 

A series of monodisperse, 1,3,5-phenylene-based dendrimers (62) and their fluorinated analogues were obtained at the AT T Laboratories [96]. These materials consist of 4, 10, 22 or 46 benzene rings linked symmetrically. In contrast to the former procedure, they are prepared stepwise. A palladium-catalyzed coupling of arylboronic acids with 3,5-dibromo-(trimethylsilyl)-benzene is used. The aryltrimethylsilane is subsequently converted to a new arylboronic acid and the next step is performed. Coupling of arylboronic acid dendrimer arms to 1,3,5-tribromobenzene or 1,3,5-tris(3,5-dibromophenyl)benzene is the final step of the synthesis. The largest hydrocarbon dendrimer is soluble to the extent of 190 g/L in toluene and is stable to 500°C. 

Wide spectrum of fluorinated aromatic compounds has been synthesized by electrophilic fluorination of arylboronic acids. So 3-fluoropyridine (63) has been obtained from 3-pyridine boronic acids 86 and F-TEDA-BF4 in 72 % yield [76] (Scheme 32). 

SCHEME 7.55 Silver-mediated fluorination of arylboronic acids [92]. 

In addition to arylboronic acids, arylboronates have also been successfully used in fluorination reactions (Scheme 7.56) [93]. These boron compounds are attractive substrates since they are typically more robust than other boron species and can often be stored for long periods of time. The catalyst system for this reaction was a copper(I) triflate species along with 2 equiv of silver fluoride. While several sources of electrophilic fluorine generated the aryl fluorides, N-fluoro-2,4,6-trimethylpyridinium hexafluorophosphate was the most effective. The chemistry displayed broad functional group tolerance with the lowest yields obtained with heteroarylboronates. The authors were also able to devise a one-pot borylation-fluorination reaction starting from the parent arene. The arene was converted into an arylboronate through an iridium-catalyzed borylation reaction in the first step of the reaction, while fluorination was achieved during the second step. This is particularly attractive since it facilitates the conversion of unfunctionalized substrates into aryl fluorides. 

The silver-promoted fluorination of bulky arylboronic acids would be a good place to start. The chemistry generates bulky aryl fluorides in moderate to high yields [92]... 

Much effort has been made to exploit the use of this reagent in the construction of fluorinated compounds. For example, treatment of 2-BrTFP with various arylboronic acids in the presence of PdCl2(PPh3)2, KOH, and AsPha at ca. 70°C for 10-12 hours gives the corresponding a-(trifluoromethyl) styrenes in high yields (Path A, Scheme 26.40). °... 

---