Synthesis and characterization of terbium doped TiO₂ nanoparticles and their use as recyclable and reusable heterogeneous catalyst for efficient and environmentally sustainable synthesis of spiroannulated indolo[3,2‐c]quinolines‐ mimetic scaffolds of isocryptolepine

Abstract

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.

Chiral Phosphoric Acid-Catalyzed Pictet–Spengler Reactions for Synthesis of 5′,11′-Dihydrospiro[indoline-3,6′-indolo[3,2-c]qui-nolin]-2-ones Containing Quaternary Stereocenters

“…2-(1 H -Indolyl)­aniline derivatives 1a and 1b were prepared according to known methods. − 2-(1 H -Indolyl)­aniline derivatives 1c – 1g could be prepared according to the reported methods with minor modification. − 2-(3,5-Dimethyl-1 H -pyrrol-2-yl)­aniline 1h could be synthesized from 2,4-dimethyl-1 H -pyrrole and 2-nitrobromobenzene in two steps according to a similar report. , Among them, compounds 1a and 1b are the known compounds. , …”

“…As the N -H of indole usually plays a crucial rule in controlling the activity and enantioselectivity, ,,, we first evaluated the influence of N -H. To our delight, when 2-(1-benzyl-1 H -indol-2-yl)­aniline 1a was tested under our previous optimal conditions, the enantioselectivity was significantly increased to 50%. Therefore, 2-(1-benzyl-1 H -indol-2-yl)­aniline 1a and isatin 2a were chosen as model substrates for further explorations.…”