and 1,2-dimethyl-1 H-imidazol-5-amine with aryl isocyanates, α-chloroalkyl isocyanates, N-(alkoxycarbonyl)imidoyl chlorides and 2,4,6-tris(trifluoromethyl)-1,3,5-triazine leads to thiapurines and purines containing trifluoromethyl groups in the 2- and 6-positions of the pyrimidine ring.