Synthesis of pyrazole and pyrimidine Troger's-base analogues

Troger's-base analogues bearing fused pyrazolic or pyrimidinic rings were prepared in acceptable to good yields through the reaction of 3-alkyl-5-amino-1-arylpyrazoles and 6-aminopyrimidin-4(3H)-ones with formaldehyde under mild conditions (i.e., in ethanol at 50 degreesC in the presence of catalytic amounts of acetic acid). Two key intermediates were isolated from the reaction mixtures, which helped us to suggest a sequence of steps for the formation of the Troger's bases obtained. The structures of the products were assigned by H-1 and C-13 NMR, mass spectra and elemental analysis and confirmed by X-ray diffraction for one of the obtained compounds.