C. Colas et M. Goeldner, An efficient procedure for the synthesis of crystalline aryldiazonium trifluoroacetates - Synthetic applications, EUR J ORG C, (6), 1999, pp. 1357-1366
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.