Aryl fluorides, preparation with boronic

Aryl fluorides also may be prepared from arenamines by way of dia-zonium salts if the procedure is slightly modified. The amine is diazotized with nitrous acid in the usual way then fluoroboric acid or afluoroborate salt is added, which usually causes precipitation of a sparingly soluble diazonium fluoroborate. The salt is collected and thoroughly dried, then carefully heated to the decomposition point—the products being an aryl fluoride, nitrogen, and boron trifluoride ... 

The majority of the more important methods for the preparation of fluorinated compounds by substitution reactions have been reviewed in the previous sections. There are, however, some additional important synthetic procedures which should also be mentioned, mainly those concerned with the introduction of fluorine by substitution of functional groups containing boron, silicon and tin the reactions of organotin compounds are the most well-studied to date. These reactions are excellent synthetic methods for obtaining vinyl and aryl fluorides (sec also Section 1.1.1.1.). 

Thallium(III), particularly as the trifluoroacetate salt, is also a reactive electrophilic metallating species, and a variety of synthetic schemes based on arylthallium intermediates have been devised.75 Arylthallium compounds are converted to chlorides or bromides by reaction with the appropriate cupric halide.76 Reaction with potassium iodide gives aryl iodides.77 Fluorides are prepared by successive treatment with potassium fluoride and boron trifluoride.78 Procedures for converting arylthallium compounds to nitriles and phenols have also been described.79... 

Oxidative fluorodesulfuriztuion can also be achieved by the action of nitrosonium tetrafluo-roborate, as oxidant, and hydrogen fluoridc/pyridine, as a source of fluoride ions, on aryl sulfides. The starting compounds are easily prepared from ketones or aldehydes and ben-zenethiol using boron trifluoride monohydratc as catalyst, and subsequent reduction with triethylsihine. - ... 

For synthesis of ary fluoride is added to the Suzuki and StUU t the catalytic system c prepared by coupling o the other terminus, and accomplished with in s For access to aryl boron or that of aryl iodides ... 

Another solution is to employ trifluoroborate salts 2.215, which can be prepared from the boronic acid by treatment with potassium hydrogen fluoride (Scheme 2.74). They can also be prepared from alkyl bo-ranes in a similar way (Scheme 2.75). These stable salts can be efficiently employed in Suzuki coupling reactions (Scheme 2.T6)P One application is in the synthesis of the unusual amino acid, trityrosine 2J26 (Scheme 2.77). In this synthesis an aryl diiodide 2.222 was coupled with a trifluoroborate salt 2.224 that had been formed by Miyaura borylation of iodide 2.223 followed by KHF2 treatment. Global debenzylation of coupling product 2.225 gave the product 2.226. Another example of the use of a trifluoroborate salt can be found in Scheme 2.88. 

The biaryl moiety of proteasome inhibitor TMC-95 has been prepared via a ligandless Pd(OAc)2-catalyzed Suzuki-coupling reaction of 7-iodoisatin with steri-cally hindered tyrosine-derived aryl boronic acid using potassium fluoride as a... 

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