Hydrogen fluoride diazonium salts

In a heated, stirred reactor, with overflow, in which the diazonium salt is fed with a heat-exchange medium which can be fluorobenzene (for dediazoniation temperatures up to 80°C) or a hydrogen fluoride/sodium fluoride/water mixture (HF/ NaF/H20 15.0 0.75 1.5 mol/mol).73 74 This method has been improved with a cascade of two reactors, with 90% of the reaction being done in the first reactor.75... 

Other photoinduced fluoro-dediazonizations have been described, and in some cases excellent yields of aryl fluorides are obtained as shown for 18 and 19.26 In these examples the aryl diazonium salts were prepared using 3-methylbutyl nitrite in boron trifluoride etherate and hydrogen fluoride (1 l).27... 

Diazonium salts were also used in the synthesis of all stereoisomers of centrolobine (Scheme 5.11). After formation of a dihydropyran by RCM-alkene isomerization (see Section 8.3.10), a Heck reaction with the p-methoxyphenyl diazonium salt 5.40 occurred trans to the side chain, with the expected alkene migration (Section 5.1.6). Hydrogenation of the alkene 5.41, followed by deprotection using fluoride gave the unnatural diastereoisomer 5.43, while deprotection under acidic conditions gave the natural product 5.42. 

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