Synthesis and Crystallographic Characterisation of Pyridyl- and Indoleninyl-Substituted Pyrimido[1,2-b]Indazoles

Pyridyl- and indoleninyl-substituted pyrimido[1,2-b]indazole were synthesised in good to high yields from the condensation reaction of 1,3-dialdehydes with 3-aminoindazoles. The structural features of the compounds were determined by NMR (H-1, C-13 and F-19), FT-IR and HR-MS. The spectroscopic assignments were confirmed by X-ray crystallography for two derivatives, i.e., 9-Bromo-3-(pyridin-4-yl)pyrimido[1,2-b]indazole (1b) and 10-Methoxy-3-(pyridin-4-yl)pyrimido[1,2-b]indazole (1c), which further provides support for significant delocalisation of pi-electron density over the entire fused ring system. The molecular packing was assessed by conventional methods together with Hirshfeld surface analyses. In 1b, the molecular packing features pyrimidyl-N-H center dot center dot center dot N(pyrimidyl), pi(pyrazolyl)center dot center dot center dot pi(pyrimidyl) and Br center dot center dot center dot N interactions within a two-dimensional array. In 1c, pyrimidyl-C-H center dot center dot center dot N(pyrazolyl) and pyridyl-C-H center dot center dot center dot O(methoxy) interactions feature within a three-dimensional architecture.