Synthesis of a sustainable heterogeneous catalyst, titanium dioxide-loaded hydroxyapatite for functionalised chromen-dihydropyridines under green conditions

We have described the synthesis of composite materials with different titanium dioxide loading on hydroxyapatite (TiO2/HAp). Their structural properties and morphologies were established by powder X-ray diffraction (p-XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) analyses. The catalytic efficacy of the as-prepared composite materials was explored to synthesise novel 4-oxo-chromen-dihydropyridine derivatives by the four-component reaction. The one-pot fusion in ethanol medium involved chromene-3-carbaldehyde, dimethyl acetylenedicarboxylate, malononitrile and different aromatic and heteroaryl amines. The method provided impressive yields (92-97%) of the target products in a short reaction time (<21 min) at room temperature. Further, we examined the efficiency of the separated catalyst, reused up to five runs with similar catalytic activity. This sustainable protocol merits easy workup, fast reaction time, superior yields, catalyst reusability, mild reaction environment and column-free purification.