Activated Alumina Balls under Neat Conditions: A Green Catalyst for the Synthesis of Spiro‐Heterocyclic Scaffolds by Ring‐Opening versus Annulation of the Isatin Moiety

Abstract

We report a green, efficient and straightforward approach for the regioselective synthesis of new spiro‐heterocyclic scaffolds using environmentally benevolent activated alumina balls (3–5 mm diameter) as a catalyst under neat reaction conditions. The methodology is advantageous because of its short reaction time, moderate to excellent yields, easy work‐up, practical simplicity and high regioselectivity without any troublesome/hazardous disposal of the catalyst or toxic byproducts. The pore size of the catalyst plays a key role in the formation of the spiro derivatives. Specifically, we observed that the reaction yield was hardly affected by the surface area or pore volume, but surprisingly, the yield correlated directly with the pore size of the catalyst.

Engaging Isatins in Multicomponent Reactions (MCRs) – Easy Access to Structural Diversity

“…The resulting spiro[pyrrolo‐4,10’‐indeno[1,2‐ b ]quinolin]‐3‐carboxylate derivatives (21 examples) were obtained in moderate to very good yields, under solvent‐free conditions, using activated alumina balls as catalyst (Scheme 132A). The catalytic effect of the eco‐friendly activated alumina balls was directly correlated with the displayed pore size, but not with pore volume or surface area [180] . In the second example, a library of spiro[indolo‐3,10’‐indeno[1,2‐ b ]quinolin]‐2,4,11’‐trione derivatives (51 examples) was obtained from isatins, indane‐1,3‐dione, and different enaminones using the surfactant CTAB as catalyst (Scheme 132B) under environmentally benign conditions.…”

“…The 4‐MCR involving isatins, primary amines, indane‐1,3‐dione, and β‐ketoester allowed the preparation of the desired products (12 examples) in moderate to good yields (Scheme 94). The recyclable and reusable catalyst presented a loss of approximately 10 % activity after 10 cycles, and its mechanism of action was hypothesized to be related to the ability of the alumina balls to trap water molecules released during the reaction in its pores, driving the reaction in the direction of the spirooxindole derivatives [180] …”

“…HPA−F‐SBA‐LDH [80] SiO 2 @g‐C 3 N 4 [78] starch [88] isinglass [89] eggshell [90] Fe 3 O 4 /GO‐Mo [100] APTPOSS [101] Cs x H 3 ‐xPW 12 O 40 ‐ZZP [102] NiCo 2 O 4 @Ni(BDC) [152] activated alumina balls [180] …”

A comprehensive review on the decontamination of lead(ii) from water and wastewater by low-cost biosorbents

“…It does not swell, shrink, soften, or disintegrate throughout the adsorption process. 59 Furthermore, activated alumina has outstanding adsorption capabilities and a high ion uptake capacity, as well as being cost-effective, safe, and ecologically friendly, making it suitable for use in wastewater treatment. 60 Activated alumina has a good surface area and is frequently applied to get rid of oxygenates and mercaptans of hydrocarbons and especially, fluorides in water.…”

Silver‐Induced Cα(sp3)–H Activation of Benzylamines Followed by [1,5]‐ versus [1,3]‐Rearrangement: A Strategy towards the Regioselective Synthesis of Spiro‐Dihydropyrroles

“…Therefore, the exploration of more general and viable routes for the improvement of synthetic efficiency remains an attractive goal. As part of our continuing efforts towards the development of spiro‐heterocycles through multicomponent approaches, we hereby demonstrate a silver(I)‐induced C α (sp 3 )–H bond functionalization of benzylamines followed by chemo‐ and regioselective [1,5]‐rearrangement (versus the alternative [1,3]‐rearrangement reaction strategy) in the presence of dialkyl but‐2‐ynedioate and isatin for the development of multifunctionalized spiro‐pyrrole derivatives in 1,4‐dioxane (Scheme , c).…”