An efficient procedure for the synthesis of crystalline aryldiazonium trifluoroacetates - Synthetic applications

We have developed a very mild procedure for the synthesis of crystalline ar yldiazonium trifluoroacetate salts in high yields under anhydrous condition s. Over thirty mono- or polyfunctional aniline derivatives have been diazot ized by this method, including water- and acid-sensitive substrates. The o- and p-hydroxyaryldiazonium salts, derived from the corresponding anilines, could be deprotonated by treatment with K2CO3 to yield pure diazoquinones. NMR and UV/Vis spectra have been recorded for all the synthesized salts; t he data are in good agreement with the rather limited published data and co nstitute a first extensive report of C-13-NMR chemical shifts in diazonium salts. An excellent linear relationship emerged between Brown's substituent constants s(p)(+) and the C-13(ipso) chemical shifts. The diazonium salts obtained proved to be much more soluble in organic solvents than their tetr afluoroborate counterparts. They were tested in Pd-mediated coupling reacti ons of various carbon-carbon double bonds, and were found to give good yiel ds within short reaction times under very mild conditions, We believe that diazonium trifluoroacetates represent a very attractive alternative to diaz onium tetrafluoroborates.