Synthesis of Naphtho[1′,2′:4,5]imidazo[1,2‑a]pyridines and Imidazo[5,1,2-cd]indolizines Through Pd-Catalyzed Cycloaromatization of 2‑Phenylimidazo[1,2‑a]pyridines with Alkynes

In this paper, palladium-catalyzed oxidative cycloaromatization of 2-phenylimidazo­[1,2-a]­pyridine (PIP) with internal alkyne is studied. From this reaction, two classes of fused N-heterocycle, naphtho­[1′,2′:4,5]­imidazo­[1,2-a]­pyridine (NIP) and imidazo­[5,1,2-cd]­indolizine (IID), were formed t...

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Bibliographic Details
Published in:Journal of organic chemistry 2015-08, Vol.80 (15), p.7508-7518
Main Authors: Li, Peiyuan, Zhang, Xinying, Fan, Xuesen
Format: Article
Language:English
Subjects:
Alkynes - chemistry
Catalysis
Imidazoles - chemical synthesis
Imidazoles - chemistry
Indolizines - chemical synthesis
Indolizines - chemistry
Molecular Structure
Palladium - chemistry
Pyridines - chemical synthesis
Pyridines - chemistry
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Summary:In this paper, palladium-catalyzed oxidative cycloaromatization of 2-phenylimidazo­[1,2-a]­pyridine (PIP) with internal alkyne is studied. From this reaction, two classes of fused N-heterocycle, naphtho­[1′,2′:4,5]­imidazo­[1,2-a]­pyridine (NIP) and imidazo­[5,1,2-cd]­indolizine (IID), were formed through dehydrogenative coupling featured with cleavage of the C–H bonds located on different moiety of the PIP substrates. Moreover, when 5-methyl-2-phenylimidazo [1,2-a]­pyridine or 2-mesitylimidazo­[1,2-a]­pyridine was used, either NIP or IID could be obtained as an exclusive product with good efficiency. Intriguingly, Pd­(II) showed different action mode in promoting this reaction compared with Rh­(III) and led to the formation of NIP with reversed regio-selectivity for the reaction of asymmetrical alkyne.
ISSN:0022-3263
1520-6904
DOI:10.1021/acs.joc.5b01092