Aryl halides tetrafluoroborate

Good yields of chlorides have also been obtained for reaction of isolated diazonium tetrafluoroborates with FeCl2-FeCl3 mixtures.100 It is also possible to convert anilines to aryl halides by generating the diazonium ion in situ. Reaction of anilines with alkyl nitrites and Cu(II) halides in acetonitrile gives good yields of aryl chlorides and bromides.101... 

The reaction can be carried out efficiently using aryl diazonium tetrafluoroborates with crown ethers, polyethers, or phase transfer catalysts.103 In solvents that can act as halogen atom donors, the radicals react to give aryl halides. Bromotrichloromethane gives aryl bromides, whereas methyl iodide and diiodomethane give iodides.104 The diazonium ions can also be generated by in situ methods. Under these conditions bromoform and bromotrichloromethane have been used as bromine donors and carbon tetrachloride is the best chlorine donor.105 This method was used successfully for a challenging chlorodeamination in the vancomycin system. 

Heck couplings of aryl halides with alkenes in room temperature ionic liquids have been reported [44]. Dialkylimidazolium and n-hexylpyridinium hexafluoro-phosphate and tetrafluoroborate ionic liquids were used as solvents, Pd(OAc)2 and PdCl2 as catalysts, and an amine as base. Addition of ligands such as triphe-nylphosphine, tri-o-tolylphosphine, and triphenylarsine usually had a negative affect on product yield. Addition of cosolvents such as DMF was not necessary. Palladium-catalyzed Heck reactions involving aryl bromides have been performed... 

Besides the study on Suzuki cross-coupling reactions (Scheme 5) in the ionic liquid 1,3-di-n-butyl-imidazolium tetrafluoroborate ([BBIM][BF4]) catalyzed by palladium prepared in situ in a cleaning bath, Srinivasan and co-workers reported ligand-free Pd-catalyzed couplings between aryl halides and terminal alkyne ... 

Activation of Aryl Halides. Ullmann coupling of o-bromoni-trobenzene is accomplished under exceptionally mild conditions and in homogeneous solution by reaction with copper(I) triflate in the presence of aqueous NH3 (eq 41). Yields are enhanced by the presence of a small quantity of copper(II) triflate. That the reaction is diverted to reductive dehalogenation by ammonium tetrafluoroborate is presumptive evidence for an organocopper intermediate that can be captured by protonation. 

A -Arylation. Tii-tert-butylphosphonium tetrafluoroborate is frequently used as a ligand in the iV-arylation reaction of heterocycles containing N-H bonds. The transformation is usually catalyzed by palladium conqilexes and performed in the presence of an organic base such as sodium or potassium tert-butoxide. High temperatures and long reaction times are often required to reach good conversions. Aryl halides are the most frequent electrophiles for this type of arylation. 

Aryl Halide Amination. Phenothiazine has been coupled to 3,10-dibromoperylene under palladium catalysis and in the presence of tri-terf-butylphosphonium tetrafluoroborate and potassium tert-butoxide, affording the corresponding perylene-bridged diphenothiazine in modest yield (eq 15). ... 

Aldehydes can also be prepared by the carbonylation of aryl and alkenyl halides and triflate, and benzyl and allyl chlorides using tin hydride as a hydride source and Pd(Ph P)4 as a catalyst[377], Hydrosilancs arc used as another hydride source[378]. The arenediazonium tetrafluoroborate 515 is converted into a benzaldehyde derivative rapidly in a good yield by using Et.SiH or PH MS as the hydride source[379]. 

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