SNAr displacement reactions of 6-cyclohexylmethoxy-2-fluoropurine, 6-amino-2- butylsulfonyl-4-cyclohexylmethoxypyrimidine and 2-amino-6-chloropurine with substituted anilines (eg the weakly nucleophilic 4-aminobenzenesulfonamide) are dramatically accelerated in the presence of trifluoroacetic acid and occur especially efficiently in 2, 2, 2- trifluoroethanol solvent.