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An efficient and environmentally sustainable domino protocol has been presented for the synthesis of structurally diverse spiroannulated pyrimidophenazines involving a four component reaction of 2hydroxynaphthalene-1,4-dione, benzene-1,2-diamine, cyclic ketones and amino derivatives in the presence of erbium doped TiO 2 nanoparticles as a recyclable and reusable heterogeneous acid catalyst.The present synthetic protocol features mild reaction conditions with operational simplicity, excellent yield with high purity, short reaction time and high atom economy with the use of a recoverable and reusable environmentally sustainable heterogeneous catalyst.

An efficient and environmentally benign domino protocol has been presented for the synthesis of structurally diverse spiroheterocycles spiroannulated with 1,3,4‐thiadiazolo[3, 2‐a]pyrimidine involving three‐ component reaction of 2‐amino‐1,3,4‐thiadiazole, isatin/N‐methyl‐4‐piperidone/1,2‐acenaphthylenedione and carbonyl compounds catalyzed by magnetically recoverable and reusable nanocrytalline sulfated zirconia (Fe3O4@ZrO2/SO42−) under solvent free conditions with grinding at room temperature. The use of magnetically recyclable and reusable catalyst, mild reaction conditions with operational simplicity (grinding), and excellent product yields are significant features of the present synthetic protocol. Moreover, easy magnetic separation of the catalyst eliminates the requirement of catalyst filtration after completion of the reaction and the catalyst remains highly active even after recycled several times.

Structurally diverse hybrid molecules; indenopyrroloimidazoles, imidazoindoles, chromenopyrroloimidazoles and imidazopyrrlopyrimidines, have been synthesized using DES as a sustainable solvent and promoter.

An efficient and environmentally sustainable domino protocol has been presented for the synthesis of structurally diverse spiroannulated indolo[3,2‐c]quinolines involving three component sequential reaction of phenylhydrazine, o‐aminoacetophenone and cyclic ketones using nanostructured terbium doped TiO2 as recyclable and reusable heterogeneous catalyst. The nanostructured catalyst was synthesized successfully and characterized by X‐ray Diffraction (XRD), transmission electron microscopy (TEM), EDX and Fourier transform infra‐red spectroscopy (FTIR). The substitution of Ti+4 with Tb+3 and the formation of Ti‐O‐Tb bonds as a result of doping of Terbium with TiO2 NPs increases the catalytic efficiency and facilitates the reaction to provide the products in excellent yields. The present protocol with special features; operational simplicity, atom‐economy, mild reaction conditions, environmental sustainability and high synthetic efficiency with recyclability and reusability of catalyst has been reported for the first time to synthesize spiroannulated indoloquinolines and expecting to provide the library of promising new leads in drug discovery research.

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Spiroannulated hybrid molecules with privileged substructures have been synthesized by an efficient and sustainable synthetic protocol involving isocyanide-based four component reaction of benzene-1,2-diamine, 2-hydroxynaphthalene-1,4-dione, cyclic ketones and isocyanides catalyzed by recyclable and reusable nanostructured TiO 2 with Erbium(Er) doping as heterogeneous catalyst. The synthetic protocol with special features, that is, atom and step economy, operational simplicity, synthetic efficiency and superior catalytic activity with sustainability and its recyclability and reusability provided structurally diverse hybrid molecules with unique combination of privileged substructures. The present synthetic protocol will contribute significantly to drug discovery research in view of its synthetic efficiency to synthesize drug-like molecules with structural complexity. The catalyst was successfully synthesized and characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM).

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