Ligand centered redox enabled sustainable synthesis of triazines and pyrimidines using a zinc-stabilized azo-anion radical catalyst

Das, Siuli; Mondal, Rakesh; Paul, Nanda D.

doi:10.1039/d1ob02428k

Cited by 15 publications

(7 citation statements)

References 69 publications

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“…Alcohols are inexpensive, environmentally benign, and readily available from various lignocellulose-derived biomass. Catalytic functionalization of alcohols has attracted significant attention in recent years as it offers a sustainable and environmentally benign synthesis of different value-added organic molecules limiting the use of various fossil fuel resources. − In recent years, utilizing alcohols as the primary feedstock, several transition metal-catalyzed approaches have been developed to synthesize various N -heterocycles, including pyridines. − In 2013, Milstein and co-workers reported a ruthenium-catalyzed synthesis of 2,6-disubstituted pyridines by coupling γ-amino-alcohols with secondary alcohols (Scheme ). In 2017, Kempe and co-workers described the synthesis of 3-aminopyridines via an Ir-catalyzed dehydrogenative coupling of γ-amino alcohols and β-amino alcohols (Scheme ).…”

Section: Introductionmentioning

confidence: 99%

Zn(II)-Catalyzed Multicomponent Sustainable Synthesis of Pyridines in Air

et al. 2023

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Herein, we report a Zn(II)-catalyzed solvent-free sustainable synthesis of tri- and tetra-substituted pyridines using alcohols as the primary feedstock and NH4OAc as the nitrogen source. Using a well-defined air-stable Zn(II)-catalyst, 1a, featuring a redox-active tridentate azo-aromatic pincer, 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline (La ), a wide variety of unsymmetrical 2,4,6-substituted pyridines were prepared by three-component coupling of primary and secondary alcohols with NH4OAc. Catalyst 1a is equally compatible with the four-component coupling. Unsymmetrical 2,4,6-substituted pyridines were also prepared via a four-component coupling of a primary alcohol with two different secondary alcohols and NH4OAc. A series of tetra-substituted pyridines were prepared up to 67% yield by coupling primary and secondary alcohols with 1-phenylpropan-1-one or 1,2-diphenylethan-1-one and NH4OAc. The 1a-catalyzed reactions also proceeded efficiently upon replacing the secondary alcohols with the corresponding ketones, producing the desired tri- and tetra-substituted pyridines in higher yields in a shorter reaction time. A few control experiments were performed to unveil the mechanistic aspects, which indicates that the active participation of the aryl-azo ligand during catalysis enables the Zn(II)-complex to act as an efficient catalyst for the present multicomponent reactions. Aerial oxygen acts as an oxidant during the Zn(II)-catalyzed dehydrogenation of alcohols, producing H2O and H2O2 as byproducts.

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Section: Introductionmentioning

confidence: 99%

Zn(II)-Catalyzed Multicomponent Sustainable Synthesis of Pyridines in Air

et al. 2023

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“…Based on the above experimental evidence and available literature, a plausible mechanism is depicted in Scheme 8 [9b,11a,25a,b] . The catalyst 1 a undergoes a single‐electron reduction in the presence of a reducing agent i. e., KO t Bu or Zn dust, to generate the one‐electron‐reduced active species [ 1 a ] − ( A ).…”

Section: Resultsmentioning

confidence: 99%

Zn(II)‐Stabilized Azo‐Anion Radical Catalyzed Sustainable C−C Bond Formation: Regioselective Alkylation of Fluorene, Oxindole, and Indoles

Pal,

Guin,

Chakraborty

et al. 2024

ChemCatChem

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Herein we report a sustainable approach for the alkylation of ketones, 9H‐fluorene, oxindole, and indole using alcohols as the alkylating agent catalyzed by a well‐defined air‐stable zinc catalyst (1a) of a tridentate redox non‐innocent arylazo ligand, 2‐((4‐chlorophenyl)diazenyl)‐1,10‐phenanthroline (La). 2‐3 mol% of 1a efficiently produces substituted α‐alkylated ketones, 9‐alkylated fluorenes, C3‐alkylated oxindoles, and C3‐alkylated indoles in moderate to good isolated yields. In aerial condition, the formation of bis(indolyl)methane (BIMs) derivatives were observed when indoles were subjected to alkylation by primary alcohols. A few drug molecules containing BIMs were prepared in good isolated yields. The catalyst 1a exhibited good chemoselectivity during the functionalization of fluorene and indole with oleyl alcohol and β‐citronellol. A few control experiments, including deuterium labeling experiments, performed to unveil the reaction mechanism indicate that the one‐electron reduced azo‐anion radical species [1a]‐ formed in situ, acts as the active catalyst. All the redox events occur at the redox‐active aryl‐azo ligand, which acts as the reservoir of hydrogen and electrons throughout the catalytic cycle, keeping the Zn(II)‐center as a template.

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“…The coordinatively unsaturated reduced complex provides scope for alcohol coordination (which is deprotonated by t BuOK) to form 26a. This is accompanied by the abstraction of Complexes 27 and 28 also find utility in the catalytic synthesis of pyrimidines and triazines 135 via dehydrogenative functionalization of alcohols (Scheme 42) and the reaction has been proposed to proceed by an analogous mechanism. The substrate scope of this technique is shown in Schemes S38-S40.…”

Section: Perspectivementioning

confidence: 99%

“…Complexes 27 and 28 also find utility in the catalytic synthesis of pyrimidines and triazines 135 via dehydrogenative functionalization of alcohols (Scheme 42) and the reaction has been proposed to proceed by an analogous mechanism. The substrate scope of this technique is shown in Schemes S38–S40 †…”

Section: Types Of Catalysts Catalytic Pathways and Scope Of Catalysismentioning

confidence: 99%

Electron transfer catalysis mediated by 3d complexes of redox non-innocent ligands possessing an azo function: a perspective

Swatiputra,

Mukherjee,

Dinda

et al. 2023

Dalton Trans.

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Ligand centered redox enabled sustainable synthesis of triazines and pyrimidines using a zinc-stabilized azo-anion radical catalyst

Cited by 15 publications

References 69 publications

Zn(II)-Catalyzed Multicomponent Sustainable Synthesis of Pyridines in Air

Zn(II)-Catalyzed Multicomponent Sustainable Synthesis of Pyridines in Air

Zn(II)‐Stabilized Azo‐Anion Radical Catalyzed Sustainable C−C Bond Formation: Regioselective Alkylation of Fluorene, Oxindole, and Indoles

Electron transfer catalysis mediated by 3d complexes of redox non-innocent ligands possessing an azo function: a perspective

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