The solvent-free reaction between 5-amino-1H-pyrazoles and -triketones (2-acetyldimedone and 2acetylindandione) leads to the formation of new fused pyrazolo[1,5-a]pyrimidines in good yields.A possible mechanistic route is postulated on the basis of the isolation of the cyclization intermediate.The structures and regiospecificity of the reaction were determined on the basis of nmr measurements and X-ray diffraction.