Arenediazonium fluoroborates

The relative efficacy of this procedure compared with the standard Balz-Schie mann arenediazonium fluoroborate conditions for difunctional aromatics is shown in Table 66 in reference 14 and in equation 7 The arenedidzonium liexafluorophosphate... 

The Bergmann variation of the Balz Schiemann reaction is a two-step process featuring copper- or copper halide-catalyzed decomposition of aqueous or acetone solutions of arenediazonium fluoroborates containing alkyl or halogen substituents [30] A recent modification is a one-step technique featuring simultaneous diazoti-zation and decomposition by addition of aqueous sodium nitrite at 25 °C to a mixture of fluorobonc acid, copper powder, and 2 isopropyl 6 methylaniline to give 2-isopropyl-6 methylfluorobenzene in 73% yield [37]... 

Depending on structure, photolysis of films of arenediazonium fluoroborates and hexafluorophosphates at room temperature gives aryl fluorides m 10-75% yield [32] In situ photochemical decomposition of arenediazonium fluoroborates... 

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. ... 

From sodium telluride or sodium 0,0-diethyl phosphorotellurolate and arenediazonium fluoroborates... 

Sodium telluride and sodinm 0,0-diethyl phosphorotellurolate, prepared respectively by the Te/NaBH4DMF method and by the reaction of elemental tellurium with NaH and 0,0-diethyl phosphate in ethanol, react with arenediazonium fluoroborates, giving good yields of diaryl tellurides. ... 

Another method that uses arenediazonium fluoroborates to prepare diaryl tellurides is the reaction with potassium tellurocyanate. Aryl teUurocyanides are postulated as intermediates. 

The Balz-Schiemann reaction, thermal decomposition of arenediazonium fluoroborates, is still a favorite approach to the laboratory preparation of fluoro aromatics [16, 17 Caution must be exercised in handling and decomposing mtroarenediazomum fluoroborates and pyridinediazomum fluoroborates because detonations have been reported [J8, 19]... 

New diazotization techniques for the Balz-Schiemann reaction feature alter native mtrosating agents in place of aqueous sodium nitrite or substitution of other salts such as arenediazonium hexafluorophosphates tor arenediazonium fluoroborates... 

Anisylcyclohexylmethylphosphine, 31 Anthracyclinones, 254 Anthraquinones, 189-190 Antimetabolitc AT-125, 146 Aphidicolin, 558 Aplasomycin, 57-58 Ara-7-deazaguanosine, 403, 404 Arene ally la t ion, 516 Arenediazonium fluoroborates, 161 Arenesulfonyl chlorides, 429, 495 Arene(tricarbonyl)chroniium complexes, 131-132... 

Reactions with arenediazonium fluoroborates. Treatment of arenediazonium tetrafluoroborates with these nitroxides, (1) or (2), generates aryl radicals (Ar ), which can then undergo useful synthetic reactions.1 Examples ... 

Arenediazonium fluoroborates react with 3-methyl- or 3-methylene-l,2-diselenolylium salts (209) in water or alcohol to afford 6,6aA.--diselena-l,2-diazapentalenes (211). The polar solvents used appear to assist the reaction as shown in Scheme 91 (76JCS(P1)228). 

In reduction of arenediazonium fluoroborate with tributylstannane, formation of the arene takes place not only by hydrogen atom abstraction from the stannane, but also by reaction of the radical interm iate with the solvent. Reduction of 4-methoxybenzenediazonium fluoroborate with tributyltin deuteride in te-trahydrofuran or acetonitrile affords not only deuterated but also deuterium-free arenes (equation 89). There are also small amounts of biphenyl by-products. ... 

Halogen exchange with a fluoride anion is one of the two main techniques to introduce a fluorine atom on an aromatic nucleus, which is a useful complement of diazotization of anilines in hydrogen fluoride or thermal decomposition of arenediazonium fluoroborates (Schiemann reaction). It is used on an industrial scale to produce, for example, 2,6-difluorobenzonitrile (the precursor of the insecticide Diflubenzuron) or 2,4-difluoroaniline (the precursor of Diflufenican or other herbicides). 

Dithioles. Diselenoles. and Dltelluroles.- Treatment of ethyl benzoylacetate with Lawesson s reagent (188) gives the l,2-dithiole-3-thione (189) 197 the latter reacts with arenediazonium fluoroborates to yield the 1,2-dithioliua salts (190 R = aryl). The action of -methylbenzylidenemalononitrile, PhMeC C(CN)2, on the methylthio-analogue (190 R = Me) leads to a mixture of the condensation product (191) and the thieno[3,2-b]thiopyranimine (192).199 The mesoionic dithiolium oxide (193) has been prepared from -dichloroacetone and sulphur, followed by methylation. 

Only in the replacement of the diazonium group by — F need we isolate a diazonium salt. We do this by adding HBF4 to the mixture, causing the sparingly soluble and reasonably stable arenediazonium fluoroborate, ArN2 BF4, to precipitate. 

Schiemann Reaction (Section 23.8E) Heating an arenediazonium fluoroborate is the most common synthetic method for introduction of fluorine onto an aromatic ring. 

A high-yield conversion of arenediazonium fluoroborates into the corresponding arylhydrazines occurs in methylene chloride, using benzeneselenol, PhSeH, while the reaction of diazonium salts with Janovsky cr-complexes (180) formed from m-dinitrobenzene and MeCOCH gives (181) and (182) by displacement of the nitro-group with the diazonium residue (Scheme 28). 

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