Synthesis of pyrazole and pyrimidine Tröger's-base analogues

Abstract

Tröger'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 °C 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 Tröger's bases obtained. The structures of the products were assigned by ¹H and ¹³C NMR, mass spectra and elemental analysis and confirmed by X-ray diffraction for one of the obtained compounds.