The scope and limitations of the use of the palladium-catalyzed
cross-coupling reactions of diverse alkyl- and aryltrifluoroborates
with halopurines have been studied. While aryl- and hetaryltrifluoroborates
reacted readily with both 6-chloropurines and 8-bromoadenines to
give the corresponding 6- or 8-aryl derivatives in high yields,
the alkyltrifluoroborates were much less reactive and, even after
thorough optimization, only methyl- and cyclopropyltrifluoroborates
gave moderate yields of the desired alkylated purines, while other
alkyl-, dialkylaminomethyl- and ethoxycarbonylethyltrifluoroborates
did not give any reaction.
purines - cross-coupling reactions - organotrifluoroborates - palladium - phosphine ligands
