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. 2022 May 26;12(25):15834-15847.
doi: 10.1039/d2ra01752k. eCollection 2022 May 23.

Study and application of graphene oxide in the synthesis of 2,3-disubstituted quinolines via a Povarov multicomponent reaction and subsequent oxidation

Samantha Caputo  1 , Alessandro Kovtun  2 , Francesco Bruno  3   4   5 , Enrico Ravera  3   4   5   6 , Chiara Lambruschini  1 , Manuela Melucci  2 , Lisa Moni  1
Affiliations

Study and application of graphene oxide in the synthesis of 2,3-disubstituted quinolines via a Povarov multicomponent reaction and subsequent oxidation

Samantha Caputo et al. RSC Adv. .

Abstract

The carbocatalyzed synthesis of 2,3-disubstituted quinolines is disclosed. This process involved a three-component Povarov reaction of anilines, aldehydes and electron-enriched enol ethers, which gave the substrate for the subsequent oxidation. Graphene oxide (GO) was exploited as a heterogeneous, metal-free and sustainable catalyst for both transformations. The multicomponent reaction proceeded under simple and mild reaction conditions, exhibited good functional group tolerance, and could be easily scaled up to the gram level. A selection of tetrahydroquinolines obtained was subsequently aromatized to quinolines. The multistep synthesis could also be performed as a one-pot procedure. Investigation of the real active sites of GO was carried out by performing control experiments and a by full characterization of the carbon material by X-ray photoelectron spectroscopy (XPS) and solid-state nuclear magnetic resonance (ssNMR).

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Conflict of interest statement

There are no conflicts to declare.

Figures

Scheme 1
Scheme 1. Syntheses of 2,3-disubstituted quinolines 2via the Povarov multicomponent reaction and subsequent oxidation.
Scheme 2
Scheme 2. Scope of the carbocatalyzed Povarov reaction. Different reaction conditions: (a) rt, 24–48 h; (b) 60 °C, 24–48 h; (c) CH3CN/H2O = 4 : 1, 60 °C, 24–48 h.
Scheme 3
Scheme 3. Scale-up experiment.
Fig. 1
Fig. 1. Recyclability experiment for the carbocatalyzed Povarov reaction.
Fig. 2
Fig. 2. XPS C 1s signal of: (a) commercial Graphenea GO; (b) GO after CH3CN at room temperature for 24 h; (c) GO after the 1st cycle; (d) GO after the 6th cycle.
Fig. 3
Fig. 3. (a) Nitrogen vs. reaction efficiency and (b) chlorine vs. reaction efficiency.
Fig. 4
Fig. 4. CP 1H–13C ssNMR signals of commercial Abalonyx GO after CH3CN at room temperature for 24 h; GO after the 1st cycle; GO after the 3rd cycle.
Fig. 5
Fig. 5. 1H–13C correlation ssNMR signals of commercial Abalonyx GO after CH3CN at room temperature for 24 h (a); GO after the 1st cycle (b); GO after the 3rd cycle (c).
Scheme 4
Scheme 4. Proposed catalytic activities of GO in the Povarov reaction.
Scheme 5
Scheme 5. Investigation of the oxidation mechanism and control experiments.
Scheme 6
Scheme 6. Scope of the oxidation of THQs in the presence of GO.
Scheme 7
Scheme 7. Synthesis of oxepin-annulated quinolines 4.
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