Pyrazolo-fused 4-azafluorenones as key reagents for the synthesis of fluorescent dicyanovinylidene-substituted derivatives

A green process to access pyrazolo-fused 4-azafluorenones (indeno[1,2-b]pyrazolo[4,3-e]pyridines, IPP) 4a–xvia the three-component reaction between indan-1,3-dione (1), benzaldehydes 2 and 5-amino-1-arylpyrazoles 3 is described. These compounds were successfully used as precursors of the novel dicyanovinylidene derivatives 7a–d containing different acceptor (A) or donor (D) aryl groups at position 4 of its fused system. The structures of products obtained (4a–x and 7a–d) were determined based on NMR experiments, HRMS analysis, and X-ray diffraction studies for 7b. The photophysical and computational studies of 7a–d showed that these products are modulable ICT fluorophores, even some preliminary tests revealed that these compounds could be used as fluorescent chemodosimeters for cyanide detection.