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One-pot synthesis of tetracyclic fused imidazo[1,2- a ]pyridines via a three-component reaction

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ABSTRACT

A novel three-component reaction has been developed to assemble biologically and pharmaceutically important tetracyclic fused imidazo[1,2-a]pyridines in a one-pot fashion utilizing readily available 2-aminopyridines, isatins and isocyanides. The three-component coupling proceeds through the Groebke–Blackburn–Bienaymé reaction followed by a retro-aza-ene reaction and subsequent nucleophilic reaction of the in-situ generated imidazo[1,2-a]pyridines bearing an isocyanate functional group.

No MeSH data available.


Mechanistic rationale for the MCR [36].
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Figure 2: Mechanistic rationale for the MCR [36].

Mentions: A possible mechanism for the MCR is proposed in Fig. 2. The MCR proceeds through the formation of a protonated imine species from 2-aminopyridine and isatin which then undergoes a formal [4 + 1] cycloaddition with isocyanide to generate a spiro intermediate b. The spiro compound then undergoes a retro-aza–ene reaction via a [1,5]-hydride shift resulting in an aromatic imidazo[1,2-a]pyridine having an isocyanate functional group. A further intramolecular nucleophilic reaction of the imidazole and the newly generated isocyanate provides the final product 1. Noteworthy, the benzodiazepinone-fused imidazo[1,2-a]pyridine 5 was not observed which may be due to the strain of the seven-membered ring.


One-pot synthesis of tetracyclic fused imidazo[1,2- a ]pyridines via a three-component reaction
Mechanistic rationale for the MCR [36].
© Copyright Policy - Beilstein
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4979633&req=5

Figure 2: Mechanistic rationale for the MCR [36].
Mentions: A possible mechanism for the MCR is proposed in Fig. 2. The MCR proceeds through the formation of a protonated imine species from 2-aminopyridine and isatin which then undergoes a formal [4 + 1] cycloaddition with isocyanide to generate a spiro intermediate b. The spiro compound then undergoes a retro-aza–ene reaction via a [1,5]-hydride shift resulting in an aromatic imidazo[1,2-a]pyridine having an isocyanate functional group. A further intramolecular nucleophilic reaction of the imidazole and the newly generated isocyanate provides the final product 1. Noteworthy, the benzodiazepinone-fused imidazo[1,2-a]pyridine 5 was not observed which may be due to the strain of the seven-membered ring.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

A novel three-component reaction has been developed to assemble biologically and pharmaceutically important tetracyclic fused imidazo[1,2-a]pyridines in a one-pot fashion utilizing readily available 2-aminopyridines, isatins and isocyanides. The three-component coupling proceeds through the Groebke–Blackburn–Bienaymé reaction followed by a retro-aza-ene reaction and subsequent nucleophilic reaction of the in-situ generated imidazo[1,2-a]pyridines bearing an isocyanate functional group.

No MeSH data available.