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An efficient, environmentally benign isocyanide-based domino protocol is presented for synthesizing spiroheterocycles with 2-amino benzothiazole/1,3,4-thiadiazole, cyclohexyl/tert-butyl isocyanides and isatines/cyclic carbonyls, catalyzed by recyclable nanocrystalline TiO2.

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An efficient and environmentally benign one-pot four-component domino protocol has been presented for the synthesis of structurally diverse spirooxindoles spiroannulated with pyrazolopyrimidophthalazines, indenopyrazolophthalazines, chromenopyrazolophthalazines and indazolophthalazines involving the reaction of phthalic anhydride, hydrazine hydrate, isatins and cyclic diketones/diamides in a deep eutectic solvent (choline chloride : urea: 1 : 2). The present protocol offers some advantages such as operational simplicity with easy workup, shorter reaction times, good to excellent yields with superior atom economy and environmentally benign reaction conditions.

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 diversity oriented synthetic protocol has been presented to synthesize spirooxindoles using isocyanide based multicomponent reaction in the presence of surface modified TiO2 nanoparticles as recyclable and reusable heterogeneous acid catalyst. This convergent synthetic protocol incorporates structural complexity and molecular diversity in molecular structures with atom economy, synthetic efficiency and operational simplicity in a time and cost‐effective manner. The recyclability and reusability of the catalyst make the present synthetic protocol economically viable for industrial processes.

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.

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