Diazonium fluoroborates

The Bart reaction has now been extended to the synthesis of arylphosphonic acids by the interaction of the diazonium fluoroborate and phosphorus trichloride (Doak and Freedman, 1951). 

A standard way to form the aryl diazonium fluoroborate salt is to add fluoroboric acid (HBF4) or a fluoroborate salt to the diazotization medium... 

Diazotization of an arylamine followed by treatment with fluoroboric acid gives an aryl diazonium fluoroborate salt Heating this salt converts it to an aryl fluoride... 

Schiemann reaction (Section 22 17) Preparation of an aryl fluonde by heating the diazonium fluoroborate formed by addition of tetrafluorobonc acid (HBF4) to a diazonium ion Schiffs base (Section 17 10) Another name for an imine a compound of the type R2C=NR ... 

The Balz-Schiemaim reaction is a useful laboratory and industrial method for the preparation of fluoroaromatics. The water-insoluble diazonium fluoroborate is filtered, dried, and thermally decomposed to give the aryl fluoride, nitrogen, and boron trifluoride (28—30). 

Nitroimidazoles and 2-azidoimidazoles are available via the diazonium fluoroborates, and photolytic decomposition of the fluoroborates gives 2-fluoroimidazoles (80AHC(27)24i). 

Arenediazonium hexafluorophosphates represent a promising alternative to diazonium fluoroborates because of decreased water solubility and, in some instances, higher yields of fluoroaromatics [27, 28] (equation 6)... 

Preparation of aryl fluorides Addition of fluoroboric acid to a solution of a diazonium salt causes the precipitation of an aryl diazonium fluoroborate. When the dry aryl diazonium fluoroborate is heated, an aryl fluoride results. This is the Schiemann reaction it is the most general method for the preparation of aryl fluorides. 

In a general procedure the arenediazonium fluoroborate is isolated, and then heated without solvent. A modern variant permits the photochemical decomposition without initial isolation of the diazonium fluoroborate. ... 

There have been few reports of indole fluorination. 2-Methylindole was largely destroyed by cobalt(V) fluoride treatment, giving perfluorocyclo-hexane and perfluoromethylcyclohexane among the products [70MI2 72HC(25-2)127]. 4-Fluoro-3-indoleacetonitriles have been prepared from the diazonium fluoroborates (85CPB3696). 

The only approaches to fluorinated indazoles seem to be via the diazonium fluoroborates [77BSF171 90AHC(48)65]. 5-Fluoroindazole has been nitrated (92PHA22). 

Fluorination. Attention has been focused on the direct fluorination of isoquinolines activated by conversion into 2-methylisocarbostyril (80). With gaseous fluorine (diluted to 10% with argon) in acetic acid a 54% yield of the 4-fluoro derivative was obtained. (Scheme 40). With methylene chloride as the solvent, only the 4-chloro analogue was formed [82H( 17)429]. Fluoroisoquinolines have also been made by displacement of nitro groups, and from diazonium fluoroborates (87JHC181). Hepta-chloroisoquinoline was converted into a perfluoro derivative by heating it in an autoclave with anhydrous potassium fluoride [66JCS(C)2328]. 

Diazonium salts react with oximes to give aryl oximes, which are easily hydrolyzed to aldehydes (R = H) or ketones." A copper sulfate-sodium sulfite catalyst is essential. In most cases higher yields (40-60%) are obtained when the reaction is used for aldehydes than for ketones. In another method for achieving the conversion ArNj —> ArCOR, diazonium salts are treated with R4Sn and CO with palladium acetate as catalyst. In a different kind of reaction, silyl enol ethers of aryl ketones, Ar C(OSiMe3)=CHR, react with sohd diazonium fluoroborates, ArNj BF4, to give ketones, ArCHRCOAr. " This is, in effect, an arylation of the aryl ketone. 

Carboxylic acids can be prepared in moderate-to-high yields by treatment of diazonium fluoroborates with carbon monoxide and palladium acetate or copper(II) chloride. The mixed anhydride ArCOOCOMe is an intermediate that can be isolated. Other mixed anhydrides can be prepared by the use of other salts instead of sodium acetate." An arylpalladium compound is probably an intermediate." ... 

Reaction between diazonium fluoroborates, CO, and an acid salt... 

Reaction of aryl organometallic compounds with halogens Aryl halide exchange halo-denitration halo-dehydroxylation Reaction between diazonium salts and iodide ion Heating of diazonium fluoroborates (Schiemann)... 

Replacement by -NO2 group When diazonium fluoroborate is heated with aqueous sodium nitrite solution in the presence of copper, the diazonium group is replaeed by -NO group. 

Imidazole-2-diazonium fluoroborate is an irreversible blocker of the phencyclidine binding site of the nicotinic cholinergic receptor, and it is only effective when the receptor is in a desensitized state, at variance with other aryldiazonium salts (85MI1). 

Diazonium fluoroborates, synthesis and decomposition, 5, 4 Diazonium salts ... 

The Pschorr cyclization of the diazonium fluoroborate from A-methylanthranilamide can be used to make iV-methylphenanthridinone (67JCS(C)1513). 

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